4) Insects and diseases of plants

In this tip:

  • A)# Onions
  • B)# Leek
  • C)# Potatoes
  • D)# Cauliflower
  • E)# Tomatoes
  • F)# Witloof (Chicory)
  • G)# Carrots


In this post you’ll find a description of some plant diseases and insects that I saw in my garden.  I added some photos.  Info from internet and my own experience.


A)# Onions

In early summer (June) it can happen that “many onion plants in your garden are ill”. See photos and descriptions below.

A1) Onion fly

Leaves of the onion plants are yellow – brown and lie on the garden soil.

In the onions there are maggots of the onion fly. Onion plants will die.


A2) Leaf-miner fly (on onion plants)

Leaves of the onion plants are green and curled.

In the onion you see “eating grooves” and maggots or brown pupae.

The onions will grow to big ones with deviating shape as shown on the photo above.


A3) Help against onion flies and/or leaf miner flies.

  • Buy many onion sets (more then calulated).
  • Plant only few onion sets in early spring (March and April). In these months, there is big risk of attack by leaf miner flies and/or onion flies.
    • Leaf miner flies lay their eggs on leeks and onions in March and April (early spring), as mentioned in this internet article  .
    • More about the leaf miner fly on this     site
  • But……you can plant “many” onion sets in March and April (early spring) when you put a layer of hay on the soil between and around the small onion plants. Due to the layer of hay, the soil does not dry out so fast. And there is less attack by the onion flies and miner flies. See chapter  A5).
  • Plant most onion sets in mid spring (early May). The leaf miner flies are not active during that time. Putting hay around and between the small onion plants works well too; soil does not dry out fast.
  • Harvest the onions in July to September (late summer, early fall). Onions are big enough then. Leaves get yellow and topple and the onions do not grow thicker anymore.


A4) Does it help?

The first row contains onion plants from onion sets that were planted in early spring (April). Many onion plants have been attacked by onion flies or leaf miner flies.

Two rows of onion plants from sets planted at mid spring (May 15). All onion plants look healty. At the end of August (late summer) they have grown into normal sized onions.

Conclusion: onion sets planted in May (mid spring) give a good harvest in August (late summer). And there is little attack by insects.


A5) A layer of hay around and between the onion plants:

When you have planted onion sets in early spring (March, April), you better lay some dry hay or mowed short grass between and around the little onion plants. The soil will not dry out so fast, the onion plants grow well and show less diseases and damage of onion flies or leaf miner flies.

You can always put dry hay on the soil between and around the onion plants. That works well always.


A6) Test: planting date and hay around.

A6a) Experiment

To find out when onion flies or leaf miner flies lay their eggs on onion plants, the following experiment has been executed;

  • At March 20, one onion set has been planted in the garden soil, in a small furrow. Each subsequent day, another onion set was planted in that furrow.
  • At May 1, the 43th onion set was planted. The row was full then.
  • From the beginning of April on, a thin layer of dry hay has been put around and between the onion plants that were visible. (My experience;  there is less attack of flies when there is dry lawn grass (short hay) on the soil around the onions. Hay is for sale in a pet shop and not expensive.


  • One year later, the experiment has been repeated with 3 rows of onion sets. In two rows there was dry hay between and around onion plants, in the other row there was dried grass or dry straw.


A6b) Results and conclusions:

  • No (or little) attack by the leaf miner fly or onion fly observed.
  • A few plants showed curled leaves, the harvested onions look normal.
  • Harvest: 38 onions out of 43 sets and 115 onions out of 129 sets. Many big onions and a few small onions.
  • Under the layer of hay (or straw), the soil does not dry out fast and the onion plants grow better (faster).
  • Hay around onion plants works well against attack by onion fly and leaf miner fly, even during the “risk period” of the leaf miner fly (March and April).
  • Hay around onions give more and bigger onions than dried grass or straw around onions.
  • The last 6 planted onions in each row showed no attack by flies, no curled leaves and no vermin.

More and detailed info at chapter E)# of tip 5) Planting onions in a small furrow.



B)# Leek

B1) Curled leaves

In early summer (June) some leek plants can have curled leaves. Similar to the curled leaves of the onions caused by the leaf miner fly.

There are no maggots or pupae.  Only white eating grooves in the green leaves. As indicated between the 2 red arrows. This attack is caused by leaf miner flies.


 Help against curled leaves:

  • Do not plant out the leeks that have been attacked.
  • Sow more leek seeds so you have more leeks to plant out later.
  • Grow small leeks in your garden under a tunnel greenhouse with ultra fine mesh netting at both ends of the tunnel. Experiment spring 2019. Results not yet known.


B2) Purple spots on leaves

In autum, leaves of leek plants can look like this.

This disease is called purple blotch. The leaves have purple spots. The leaves have “dead ends”. After removing the coloured leaves, the plants are okay. Leek harvest is smaller.

Info on the internet, see     this site

This disease occures after a cold and wet weather period. Maybe after planting leeks too deep or too much manure added.

The disease occured in my garden (for the very first time in more than 25 years) in 2012.


Help against purple spots:

  • Internet: Shallow planting. Adding less manure. Putting garden earth around the plants not until the plants are big.
  • My experience: Put leek plants in round holes (diameter 6 cm, 2.4 inch) in the garden soil. Keep the holes “open” for a long time. This results in no risk or little risk of this disease.


B3) Brown pupae (leaf miner fly)

Brown pupae in leeks frequently occurs. Almost every veggie gardener has seen the brown “things” on and under the leafs of a leek. There are cracks and tears in the outer white leaves of a leek. The edges of the cracks are light brown. In this chapter you find an extensive description about this attack (and how to reduce this attack).

Typical for this disease (see photos above):

  • Some (white) parts of the leek plant have long “cracks” or “tears” with light brown edges.
  • Eating tracks are visible on leaves and white parts.
  • Pupae hide in leaves or at other parts of the plant.
  • Pupae are about 4 mm long (1/6 inch) and dark or light brown. On the lowest photo at the right you see a maggot (or small pupae) that is somewhat smaller.

  • Sometimes there are some maggots on the leek. This maggot is still eating leek material. It is not yet ready to transform into a brown coloured pupa. The lowest photo with a wooden cocktail pick shows the size of the maggot.

These pupae and maggots are children of the “allium leaf miner flies” also called “leaf miner flies”. You can find info about this disease on the internet, for example on    this site   .


Leaf miner flies lay their eggs on the leaves of the leek plants in spring (early March to early May). Eggs –> white maggots –> brown puppae. The pupae “rest” until the end of summer. During this rest period, the pupae are in the leek plants (or somewhere else, such as in the garden soil or in leaves of leek or in compost).

In the end of summer, and the beginning of autumn (end of August to end of October), the miner flies hatch from the pupae. These new miner flies lay their eggs on the leaves of (new) leek plants. The pupea from these flies overwinter in the leek plants (or in the soil, leaves or compost). In spring new miner flies hatch from these pupae.

So there are 2 periods when leaf miner flies lay their eggs on leeks; in spring and in late summer/early autumn.


Help against leaf miner flies

In spring and in late summer/early autumn, you have to prevent the leaf miner flies from laying eggs on the leeks;

  • In spring you can sow or plant leek in a “flyproof” tunnel greenhouse and let hem grow bigger there.
  • In late summer/early fall you can trim the leaves of the leeks. You can also lay dry hay on the trimmed hay plants.

Below an extended description of these 2 procedures.


  • In spring; grow leek in a “flyproof” tunnel greenhouse

You can sow leeks indoors (e.g. in shove trays) at late fall to early winter (November, December). Replant the small thin long leek plants in the garden soil under a “flyproof” tunnel greenhouse, from late winter to early spring (March, April). Replant the leeks or shove blocks of soil with small leek plants on/in the garden soil. More info   tip 18)  .

Or sow leek in the garden soil under a “flyproof” tunnel from March (late winter) on.

Planting or sowing leek and using a “flyproof” tunnel is as follows;

  • Put the tunnel greenhouse on the garden soil.
  • Open the tunnel or remove it temporary.
  • Sow or replant the leeks in planting beds that are about 5 centimeters (2 inch) lower than the garden soil level. That’s easy when watering; you can let water flow in the lowered planting beds. More info further in this chapter.
  • Then put the tunnel greenhouse over the planting beds again. See 2 photos above; upper photo of April 1 (early spring), lower photo of April 28 (mid spring).

  • Close the tunnel with 2 special end plates. Each end plate is a piece of perspex with a round air hole in it. There is net curtain with small holes over each plate. Further on more info.
  • Shove some garden earth against the sides of the tunnel. To have no openings between tunnel and garden soil.
  • Keep the tunnel closed “always” (as long as possible). When opening the tunnel, the leaf miner fly can enter the tunnel and lay her eggs on the plants.

  • You can put 90° electrical conduit elbows in the garden soil at one long side of the tunnel. Water the plants under the tunnel via these elbows. Water flows via a funnel and via the elbow on the bottom of the planting bed.
  • When opening the tunnel is necessary, first remove one end plate. When the tunnel has been closed or has been put back on the soil, put the end plate against the tunnel again.

  • At very sunny weather, put a (white) piece of blanket before the tunnel greenhouse. Otherwise the temperature in the tunnel gets too high for the plants.
  • Use clothes pegs or clamps to fasten the blanket to bamboo sticks or to the end plates.


Info about the end plates;

  • There is curtain material on my end plates. I have got this net curtain from an acquaintance. The net curtain material has many tiny holes. The material is well air permeable; you can easily blow air through 2 layers of curtain material. Small insects, like miner flies or leek flies, can not pass this material.
  • Instead of this material, you can use other net curtain material with tiny holes. The holes must be smaller than 0.8 millimeters (1/30 inch), as found on the internet.

  • Each end plate is a rectangular piece of perspex, with a round air hole. The curtain material has been “folded around the plate”, tightened and fixed using screws. So there is curtain material at both sides of the end plate. More info about this topic furter in this chapter.
  • Two thick bamboo sticks and a half paving stone pushes each end plate against the tunnel.

  • You can put an extra (closed) piece of perspex (between the bamboo sticks and the paving stone) at cold weather or cold wind. See yellow arrows on the photos above. The arrow points to the closed perspex plate.
  • The extra plate shields the air opening in the end plate and holds the cold wind outside the tunnel.
  • (At freezing weather, you can lay plastic foil over the tunnel and lay bricks on the foil against blowing away).
  • Remove the closed plate at “good” weather.

  • The curtain material is at both sides of the end plate;
    • This procedure is easy and less screws needed.
    • At the outer side of the plate, the curtain holds the the insects (miner flies).
    • At the inner side, the (soft) curtain material is pressed against the hard end of the bent corrugated plate. Thanks to the curtain material, the end plate seals better against the corrugated plate. There are very narrow openings (slits) between tunnel and end plate. The leek fly or leaf miner fly can not pass these slits.
    • My end plates have 2 layers of curtain material over the air openings. My curtain material is well air permeable; you can easily blow air through 2 layers of curtain material.

When you have curtain material that is less permeable, you can cut one round hole in one layer of curtain material. This hole is right before and just as big as the air opening in the plate. Below a description.

Put this end plate with cut opening (in the curtain material) towards the tunnel. Now there is only one layer of curtain in the air opening. Still there is still soft curtain material against the side of the corrugated plate.

The above mentioned construction makes the tunnel greenhouse very airy, but still inaccessable (impassable) for leek flies, leaf miner flies and other insects.



Below a description of making the end plates.

  • Use a piece of perspex. Thickness  is about 2 millimeter (1/12 inch). Size of the end plate is about 41 x 36 centimeters (1 ft  4 inch  x   1 ft  2 inch). Perspex can be sawed. Or you can use a cutter to make a “groove” in perspex and then break it.
  • Use a flower pot and a pen to draw a circle (15 centimeters, 6 inch diameter) on the plate. Distance between circle and edge of the plate is about 10 centimeters (4 inch).

  • Drill 4 holes (diameter ) in the plate, next to the circle;
    • Diameter of the holes is about 4 millimeters, 1/6 inch.
    • Drill the holes at “3, 6, 9 and 12 o’clock”.
    • Drill the holes next to (right at the inner side of) the circle.
    • These holes are useful when sawing the round hole in the plate using a fret saw. The saw frame of the fret saw is too short to saw all circle round. In each hole you can turn the saw frame and “reverse the saw direction”.

  • Use a fret saw (or a power jig saw) to make the round hole in the plate.

  • Making the round hole using a hand-held jig saw goes well with this type of blades;
    • Sowing goes fast; it takes about 5 minutes to saw the round hole.
    • This blade does not break (easily).
    • In each hole in the plate you can turn the saw frame and “reverse the saw direction”.

  • Use sand paper to polish the side of the round hole and the left side short edge of the plate (see photo above). Polish until there are no sharp edges or flakes.

  • This photo shows a finished end plate. You can see the air opening vaguely.
    • In the plate, 3 holes have been drilled, diameter 3 millimeters (1/8 inch). Distance between each hole and edge of the plate is about 10 centimeters (4 inch). See red arrows.
    • Use a well fitting piece of curtain material.
    • The end plate has been folded in the curtain material.
    • The curtain material has been fixed to the plate with 3 screws (bolts, rings and nuts).
  • Below a description of fixing curtain material to the plate.

  • You can use these fold back clamps when stretching and fixing the curtain.

  • And use screws and rings (M3,  3 millimeters, 1/8 inch) to fix the curtain to the plate.


  • Drill 3 holes in the plate (needed for the fixing screws);
    • Diameter of each hole is about 3 millimeters (1/8 inch).
    • Distance between each hole and edge of the plate is about 10 centimeters (4 inch). See red arrows on photo above (3 photos back).

  • Cut a piece of curtain material with the right dimensions.
  • Fold the perpex plate “well fitting” in the curtain (as shown above).
  • You can use 2 clamps to fix the corners of the curtain.

  • (Remove the 2 clamps).
  • Put the top part of the curtain “upward” (towards the fold).
  • Check if the curtain dimensions are okay. The curtain must overlap the 3 holes for about 2 to 3 centimeters (about 1 inch).

  • Put the top part of the curtain back on its original position.
  • “Stretch” the curtain material at and fix the curtain on the plate using 2 clamps.

  • Put the plate and curtain on a broad wooden board or on a piece of cardboard.
  • Open each clamp (for a short moment), put the top part of the curtain towards the fold and close the clamp again.

  • Put a wooden lath under the plate, near a clamp.
  • (When not using this lath, the clamp is on the wooden board. The perspex plate “hoovers”. When putting the point of an awl in the hole, the perspex material can burst, as shown on the middle photo of 3 photos above).
  • Put the point of an awl through the hole in the plate, through the curtain material under the plate and in the wooden lath.
  • Lift the perspex plate and the curtain material. Turn or put a bolt (with ring) from the underside; first through the curtain material, then through the hole in the plate.
  • Repeat these actions at all 3 holes.

  • One side of the curtain has been fixed to the perspex plate using screws.

  • Put the top part of the curtain back on its original position.
  • First “do” the left side edge of the curtain;
    • Tighten (stretch) the curtain material.
    • Use a pencil to mark the position where the curtain touches the end of the bolt.
    • Put a block of wood under the curtain.
    • Use an awl to make a hole in the curtain at the marked (pencil) position.
    • Put the end of the bolt in the hole of the curtain.
  • Repeat these steps at the right side edge of the curtain.
  • Repeat these steps at the middle bolt.

  • All bolts are in the curtain material and in the plate.

  • Put rings and nuts on all bolts.
  • The end plate is ready for use.
  • When desired, you can cut a round hole in the curtain to improve the air permeability. This has been described above, just before the beginning of chapter “Making”.


Remark: across and staples

This photo shows an older design. The curtain material has been put crossways on the perspex plate. At one side, both ends of the curtain have been fixed using staples (stapling in this material was hard to do). Four (4) screws fix the curtain material to the perspex plate, one screw at each corner. This construction is harder to make than the construction described above.


Watering under the tunnel

  • At each plant bed you can put a special “watering tube” in the soil.

  • Use a 90° electrical conduit elbow. The elbow on thos photo is 3/4 inch.
  • Put the elbow in the garden soil under one long edge of the tunnel, until it reaches the bottom of the plant bed. Firmly push the garden earth around the elbow.
  • Now you can water the plants in the plant bed under the tunnel.

  • Use a plastic cap, a bolt and nuts (M5,    5 millimeters diameter or simular) to make a head cap for the watering tube (to keep flies out of the tunnel greenhouse).
    • Use an awl to make a hole in the cap. Put the bolt through this hole. Put 2 nuts on this bolt.
  • The bolt and nuts make the head cap heavier, so it does not fall off or is blown away easy.

  • Use a funnel and beaker.
  • You can fix a piece of curtain material around the exit of the funnel;
    • the water flows slower on the bottom of the plant bed,
    • during watering, the leaf miner fly can not pass the funnel and can not get under the tunnel.
    • but without the curtain material around the exit of the funnel it is okay too; watering takes a short time, so little chance that a miner fly will pass.
  • Put the funnel on the watering tube.
  • Pour water from the beaker into the funnel.
  • During pouring, use one hand to keep the funnel in position.


  • You can pour water in the elbow tube, without using the funnel, but then you have to take aim properly.

  • After watering, put the head cap on the watering tube.
  • In this way the tunnel is fly-proof again.


Are leek plants good?

After May 15 (late spring) the leaf miner flie does not fly anymore. And does not lay eggs on leek plants (until August, end of summer). So it is time to open the greenhouse tunnel and to replant the leek plants. Check if the leeks have been attacked by the leaf miner fly; when attacked, the leaves are curling and deviating from normal.

In 2019 I did my first test with leeks under this tunnel greenhouse with special end plates. Below the photos.

  • The greenhouse tunnel has been removed on May 15 (late spring).
  • The upper parts of the long leek leaves are bent and a little (light) brown; they grew against the inner side of the tunnel for weeks.
  • So you better make the plant bed with leeks deeper in the soil, for example 10 to 15 centimeters (4 to 6 inch) deeper than the surrounding soil level. Then leeks have more room to grow big.

  • Five days after opening the tunnel, the leek plants have been taken out of the plant bed and put in the garden soil.
  • The top of the leaves are still a little bent and light brown.
  • After shortening the carrots and the leaves, the leeks look normal.
  • All leaves of all plants look normal, so no attack by the leaf miner fly.
  • There are many thick leeks, thicker than a pencil and a few plants that are thinner than a pencil.

  • Using a PVC tube (diameter 6 centimeters, 2   3/8 inch), round holes have been made in the garden soil. Leeks have been planted in these round holes.
  • Leek plants look normal.

On August 1 (mid summer), leeks have grown bigger.


  • In late summer to early fall

Mostly there are leeks (autumn leek or winter leek) growing in the garden soil in summer and fall . To prevent the leaf miner fly from laying eggs on the leeks, you can do as follows.

Trim the leaves of leek plants near the end of summer (September 1). From then on, trim the leaves of the leek plants weekly to keep the same leaf length as after the first trimming. See photos and description below.

  • Big and small leek plants in the garden soil at the end of summer (September 1).

  • Trim all leaves of all (big) leek plants at the end of summer (September 1).
  • Photo above; all leek plants of 3 left side rows have been trimmed. All other leek plants in this area have not been trimmed.

  • After trimming the leaves of a leek plant, it has a “Y”shape. The trimmed leaves form a narrow hand fan.
  • My line of thought:
    • Leaf miner flies lay their eggs on the outer leaves of a leek plant. That’s visible at attacked leeks; many pupae in (on) the outer leaves, few pupae on the next leaves of a leek.
    • The outer leaves of a leek plant are long, curved and have a horizontal part.
    • Miner leaf flies prefer to lay their eggs on the horizontal part of a leek leaf. From that spot on, the maggots burrow in the leaves towards the base of the leek plant.
    • On trimmed steep leaves, the miner flies do not lay eggs on. You can imagine that the fly has less “foot grip” on steep leek leaves.
    • A leaf miner fly starts looking for a non trimmed leek plant with long leaves. Once found, the miner fly lays its eggs on the horizontal parts of the long leek leaves.
    • Results: At trimmed leek plants there is little or no attack by the leaf miner fly (no or only a few maggots and/or pupae) . Leek plants with long leaves suffer from serious attack by the leaf miner fly (many maggots and/or pupae).

  • At most leek plants with trimmed leaves, there is no dry hay on.
  • As an experiment you can lay dry hay on top of some trimmed leek plants. Long leaf hay works better than short leaf hay (stays much better on the leek plants).
  • During or after laying on the hay, some hay can fall on the garden soil. No problem as long as there is still some hay on the plants. Hay on the soil also keeps the garden soil moist. That is okay.


  • After trimming, the leek plants will grow bigger again. The leek leaves grow longer and higher. Some hay can drop off the plants.
  • From now on trim the leek leaves weekly until the length of the first trimming. And lay new hay or dropped off hay on the “hay leek plants” again.
  • Repeat this weekly trimming and laying hay on until mid autumn (beginning of November).
  • Fom mid fall (early November) on, the leaf miner fly does not lay eggs anymore. So trimming (and laying hay on) is not necessary.

  • The same leek plants at November 1 (mid autumn).
  • At this time you can remove the hay from the leeks. At cold moist weather, leek plants can start rotting due to the wet hay laying on the plants.



From mid November (mid fall) on, leeks have been harvested.

On the photo above you see harvested leeks. There are 3 groups of leek. Under each group of leeks there is an indication; Nothing, Trimmed or Trimmed and hay on. Below an explanation of the groups. Click on the photo for wide screen.

  • At the left side of the photo there are leeks that have grown “normally”; no trimming and no hay on (group “Nothing”).
  • In the middle you see leeks that have been trimmed weekly (group “Trimmed”).
  • At the right side there are leeks that have been trimmed weekly and that had hay on the trimmed leaves. (group “Trimmed and hay on”).

All leeks have been rinsed in cold water to remove the clinging garden sand. At most leeks one or some outer (half or damaged) leaves have been stripped.

Below there are close up photos and descriptions per group. With info about appearance of the leeks. And how many maggots and/or pupae were found during preparation (and cutting) the leeks for a meal.


Group   “N o t h i n g”

  • Close up photo of 12 “nothing” leeks. Leeks on the photos have been turned over.
  • Almost all leeks show red/brown lines and/or bursted leaves. On some leeks there are miner fly pupae visible. At these leeks there is a serious attack by the leaf miner fly. Click on the photos for wide screen view.
  • Each leek of this “Nothing” group contained 1 or more maggots and/or pupae of the leaf miner fly.

  • At 6 leeks of the group “Nothing”, all pupae and maggots have been collected, see photo above. The 6 “Nothing” leeks contained 4 maggots and 10 pupae in total.
  • You better crush the pupae and maggots (to prevent new flies from hatching).

Later on, more leeks of the group “Nothing” have been harvested and cleaned. See photos below.

  • At 4 other leeks of the group “Nothing”, the outer (half, damaged) leaves have been removed and put in the white washing-up bowl (left side of th ephoto above).
  • The leaves in the white bowl have been rinsed in a big bucket with cold water to remove clinging garden earth (and miner pupae). The cleaned leek leaves have been put on a compost container.
  • The 4 “real” leeks have been cleaned and sliced into small leek rings when preparing for a meal. Some miner pupae have been found then.

  • The water in this bucket has been used to clean the outer (half, damaged) leaves of the leeks. During this cleaning, pupae of the miner fly have also ended up in the water.
  • You can use a kitchen sieve to “catch” the pupae in the water.

  • Some miner pupae are so lightweight that they float on the water surface, see 2 light brown pupae on the photo above. Other pupae float in the water.
  • When moving the sieve through the water often enough, you can catch (almost) all pupae.

  • The miner fly pupae that were in the 4 leeks of the group “Nothing”;
    • The 18 pupae in the left side cap have been “caught” in the water where the  outer (half, damaged) leaves have been cleaned,
    • The 2 pupae in the right side cap have been found during slicing leeks into small rings when preparing for a meal.


  • In (on) the outer damaged leaves of a leek there are many miner pupae.
  • In (on) the next leaves of a leek there are much less pupae.
  • So most miner fly eggs are laid on the outer leaves of a leek plant. Why?
  • Perhaps for this reason. The miner flies that hatch from the pupae must find their way towards the outer world. That is easiest when starting in the outer leaves and moving via cracks and tears in the outer leaves.


Group  “T r i m m e d”

  • Close up photo of 7 “Trimmed” leeks. Leeks on the photos have been turned over.
  • Leeks look well; no red/brown lines and few bursted leaves. Click on the photos for wide screen view.
  • In these 7 “Trimmed” leeks there was only 1 maggot of the leaf miner fly.

Later on, 14 more leeks of the group “Trimmed” have been harvested and cleaned. These leeks are rather thin compared to the other leeks. See photos below.

  • Eleven (11) leeks “Trimmed” show red/brown lines and/or bursted leaves (top leeks on the photo, roots to the right).
  • Three (3) leeks “Trimmed” look well (lower leeks on the photo, roots to the left).
  • Click on the photos for wide screen view.

  • All 11 “Trimmed” leeks with red/brown lines contained these 16 pupae and 1 maggots. Plus 2 pupae in rinsing water. In total 19 Miner insects in 11 leeks.
  • The 3 well looking “Trimmed” leeks contained zero maggots  and zero pupae.


Group   “T r i m m e d   a n d   h a y   o n”

  • Close up photo of 6 leeks of the group “Trimmed and hay on”. Leeks on the photos have been turned over.
  • Leeks look well; no red/brown liness and few bursted leaves. Click on the photos for wide screen view.
  • There were zero maggots  and zero pupae in the 6 leeks of group “Trimmed and hay on”.

One week later, 5 more leeks of the group “Trimmed and hay on” were harvested and cleaned. See photos below.

  • Close up photo of 5 new “Trimmed and hay on”. Leeks on the photos have been turned over.
  • Four out of five leeks look well; no red/brown lines and few bursted leaves (top 2 and lower 2 leeks). Click on the photos for wide screen view.
  • One leek has red brown lines (the middle leek on the photo above).

  • Close up photo of the middle leek.  Click on the photo for wide screen view. The leek has red/brown lines until its roots.
  • When preparing the 5 “trimmed and hay on” leeks for a meal, there were no maggots  and no pupae in the leeks.



  • At “thick” leeks with short leaves (group “Trimmed”), the leaf miner fly lays no eggs or only a few eggs. There are no or only a few maggots and/or pupae in these leeks.
  • In many “thin” leeks with short leaves (group “Trimmed”), there are more maggots and/or pupae. Possible reasons:
    • The miner fly looks for thin, slow growing leeks to lay its eggs on.
    • I did not trim my thin leeks well. At thick leeks, trimming big firm leaves goes easy. Trimming thin leeks with weak leaves is much more difficult.
  • At “thick” leeks with short leaves and hay on (group “Trimmed and hay on”), the miner fly lays no eggs or only a few eggs. There are no or only a few maggots and/or pupae in these leeks.
  • At not treated leeks (group “Nothing”, the comparison group), many eggs have been laid on. In these leeks there are many maggots and/or pupae of the leaf miner fly.



  • Weekly trimming the leaves of “thick” leek plants helps well against leaf miner fly attack.
  • At “thin” leek plants, this weekly trimming does not help so good. Don’t know why.
  • Putting hay on trimmed “thick” leeks works just as well as no hay on. Maybe putting hay on works well at thin leeks.



  • I trimmed my leek plants each week. Perhaps trimming less frequent (for example each 14 days) works well too.
  • This trimming procedure works well at thick leek plants. At thin leek plants, trimming is not so effective. And putting hay on thin leeks is harder (hay falls off).
  • Due to trimming its leaves, the leek grows slower; the plant has less green leaf material. When harvesting, the leek plant will be some thinner.
  • When sowing leek in the garden soil in early spring (April), and adding manure in the planting holes, you get many thick leeks at the end of summer (early September). The plants are big enough to trim the leaves then.


  • When you have many pupae in the harvested leek, tip   15) Storage tips    chapter I4) shows how to prepare the leek for a meal.
  • On the internet I found a procedure of “cutting back infected leek plants” right above the garden soil level. See     this      and   here    . Trimming leaves of leek plants like I do can be found in this     Dutch comment    (date, time  Zo 12 Jul 2015, 10:09 . Translation; “I have trimmed my leeks last year, advice of a gardening friend. Leeks were thick and no attack by vermin”).
  • A previous experiment showed that laying hay on the soil between leek plants do not help against the leaf miner fly. Hay on leek plants helps a little.
  • Spraying liquid nettle manure on leek plants does not help too, that’s my experience. A few hours after spraying, the smell of liquid nettle manure has disappeared. And the leaf miner flies go on laying eggs on the leek plants.


After winter storage

You can put a tunnel greenhouse of transparent corrugated plate over 1 row of leek plants, growing in the soil.

Harvested leeks of group “Nothing”. These leeks grew in the garden soil under a tunnel during winter. Harvested date; March 16 (late winter). There were no pupae of the miner fly in this leek.



C)# Potatoes

At some potatoes I see brown spots (warts).

After peeling the potatoe looks normal.

This can be caused by mixing (too much) agricultural lime through the garden earth. Potatoes grow well in slightly acidic soil.


Help:  Do not add agricultural lime in the garden soil.



D)# Cauliflower

This disease is caused by larvas of the the cabbage gall midge. Info on the internet is    here    . This midge lays eggs on cabbage plants that grow at sheltered, calm places in the garden. My attacked cauliflowers grew next to the stake beans.



Plant the cabbages on windy places in the garden.



E)# Tomatoes

E1) Brown spot at lower side of tomato

Green or ripe tomatoes can have a brown spot at the lower side (opposite the crown). This is called blossom end rot and is caused by water shortage. The tomato plant is not ill, so keep the plant in the soil. You can throw the tomato in a compost container or cut away the brown material.

My plants had this disease during the long hot summer of 2018. Never seen before.



Add a little water to the plants dayly. Better add 1 small beaker of water each day than much water once a week.


E2) Crack in tomato

When much rain water falls on the tomato plants and/or when you water the tomatoes too much, you can get tomatoes with cracks.

Tomatoes on the plants can get cracks even before they are ripe.



When you add a little water to the tomato plant each day (at dry weather), there is less risk of cracks in the tomatoes. Watering goes well when using a bucket and a small beaker. You better pour 1 small beaker of water at each plant daily. That’s better than adding a big amount of water once a week.


E3) Dark spots on fruits, stems and leaves

It is possible that you get brown coloured tomatoes and brown leaves at the plants. This plant disease is called Phytophtora.

It is probably caused by rainy weather during late summer, early autumn (August, September). Cold rain water on the plants and fruits causes the plants and tomatoes to get brown (or rot).



  • When you grow tomatoes in the open air in a backyard garden, pick all tomatoes before the end of September (end of summer).
  • Or put tomato plants in a backyard garden under a roof with open sides. To overcome rainfall from above on the plants.
  • Put tomato plants in an allotment garden under a wide roof with open sides and dew drop foil under the roof. Close the sides partly during heavy rain.
  • See also tip 7) Roof over sweet peppers or tomatoes     and  tip   8) Growing tomatoes    .


Below some photos:

Tomatoes under a roof in my backyard garden at early autumn (September 1). As you see there are a lot of “good-looking” healthy tomatoes. I counted more than 100 tomatoes hanging on 11 plants. Only 10 tomatoes hanging under the roof have brown spots. And some plants have leaves with brown spots.

When there is no roof over the tomato plants, tomatoes can get brown spots and rot during “a rainy summer and a rainy, cold autumn”.


Tomatoes in my allotment garden. Under the roof there is plastic foil to catch dew drops, so they do not fall on the tomato plants.

At dry weather the side foil is folded down.

During heavy rain the side foil is fixed to the roof.

With side foil fixed, the roof is still airy thanks to openings above and below the side foil.



F)# Witloof (Chicory)

These witloof heads don’t look healty. There are brown, sticky, short outer leaves. On the heads you see spots.

Those spots are aphids. Easily to remove with a washing-up brush under running tap water. But still a problem.



This witloof has grown on chicory roots with non removed outer leaves. Maybe the compost in the flower pot was too moist during witloof forcing too.

The left side photo shows the chicory roots before witloof forcing. On the right side photo you see chicory roots with brown short outer leaves right after breaking off the heads.



Always cut or break away the outer leaves of chicory roots before forcing witloof heads. More info in chapter  N2) of tip      24) Growing chicory    .



G)# Carrots

Winter carrots can have deep cracks.



During the growth of the carrots, the garden soil has been too dry for a long time and too moist for another long time. More info in these sites;   here   and    here    .



  • Regularly water the garden soil around the carrots.
  • Lay hay or straw around the plants on the soil; the garden soil does not dry out fast.


Preparing for a meal:

You don’t have to throw these carrots on the compost heap.

Use a kitchen knife to cut the cracked carrot in good pieces. Prepare the pieces of winter carrot in the kitchen.

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7 Responses to 4) Insects and diseases of plants

  1. Pingback: 15) Storage tips for your harvest | sjefgardentips

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  3. Pingback: 18) Growing early leek | sjefgardentips

  4. Pingback: 36) Sowing and growing leeks (various methods) | sjefgardentips

  5. Steve says:

    Great advice.
    I have problems already with my leaks leaves curling over.
    Probably too late now to do anything about it.

    • Hi Steve,
      That’s too bad.
      You can still plant your own leeks when they have a pencil thickness.
      Cut more foliage than normal before planting and plant them in big round holes in the soil. Find out if some or many (of your) leeks will grow into big normal ones.

      Or you can buy new leeks now (in a plant store or at a grower) and plant them in the garden soil.
      For next year, you know what to do to grow your own non curling plant leeks.

      Good luck, Sjef

  6. Pingback: 22) Sowing onions in a small furrow | sjefgardentips

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