Citrus Leaf Miners
Question from Dave: Thank you very much for writing your books – I read and refer to them every week. I’m trying to shift from conventional to organic gardening. All of my citrus trees have citrus leaf miner – some worse than others. I’ve spread worm castings and shifted over to chicken manure based fertilizer. Which of the beneficial insects will get the leaf miner under control?
Answer from Pat: First I want to congratulate you on making the switch from a conventional garden using synthetic fertilizers and chemical pesticides to one using natural and organic fertilizers and organic controls. The pay-off is improved health and safety for your family and pets. But the switch does take time. Your number one priority is to build up the soil so your tree will be booming with health and can fight off pests by itself. But, yes, earthworm castings help and are one arrow in your quiver of pest controls.
It will take a while for the worm castings and all your other efforts to take effect. My experience is that the effect on pests of worm castings is remarkable, but takes at least 3 weeks for the effect to work on a difficult pest such as giant white fly attacking begonias. It stands to reason that for leaf miners on citrus, not only a woody plant but indeed a tree, it would take time for the chitinase in the worm castings to become combined with soil, be drawn up through the roots of the plants and up through the cambium layer of the trunk and twigs into the leaves where it can attack the chitin in the exoskeletons of the leaf miners.
Leaf miners are a difficult pest to control because, once they have entered the leaves and the larvae are mining inside the leaf, an organic spray such as fatty-acid soap or summer oil cannot penetrate the leaves and thus cannot reach the pests. I have however had experience with controlling leaf miners, not with systemic chemical pesticides, which is the usual non-organic method of control, but with a combination of organic tactics. These work, but they do take time.
One tactic is to create an organic soil in which beneficial bio-organisms can proliferate. For citrus one of the best things you can do is improve the soil with organics and plenty of fertilizer. Follow the organic methods for fertilizing citrus on pages 63 and 64 in my book. A mature citrus tree can use as much as 1 pound of pure nitrogen a year and this can be approximated by fertilizing with blood meal or cottonseed meal or alfalfa meal and watering in thoroughly into the ground and then mulching the soil over the fertilizer. Another way to go is to mulch all your fruit trees with aged horse manure or horse manure from a good horse owner covering the ground under the trees in fall and letting the rains wash the goodness into the ground. (Be sure to have your tetanus shot up to date.) These practices will produce very healthy trees that will fight off pests. Also add kelp, humic acid, and earthworm castings. The tree will do the rest.
Meanwhile, since you no longer spray with pesticides you are also creating a heaven for the beneficials (insects, birds, and arachnids) that will help to control leaf miners along with all the other pests, even mites. It takes a while for the effects of pesticides and synthetic fertilizers to wear off and for the beneficials to begin proliferating in your garden. Be sure to provide water for them in the form of a fountain or bird baths. Encourage birds also to live in your garden. Many beneficial insects help to control the adult stages of leaf miner. Even ladybugs help since their larvae, though preferring aphids, are omnivores. There are a huge number of beneficial wasps, tiny things many of them, that hunt, kill, eat or parasitize pest insects. The more organic your garden becomes the greater number of these you will have.
One of the beneficials that kills leaf miners is a tiny wasp called Leafminer Parasitoid (Diglyphus isaea). Once you have created a good habitat for this creature you can release it in your garden, but it is already living here since many escape from greenhouses where organic growers release them.
Do not spray your tree with Spinosad even though it is touted as an organic spray. Spinosad harms bees and you want bees to visit your tree and pollinate your blossoms. Also Spinosad is not an appropriate control for leaf miner since it only attacks the adult stage of the insect and has no effect whatsoever on the larvae inside the leaf.
Pat, thank you for your comprehensive response! I ordered 3000 lacewings earlier today from gardens alive – will the worm casting tea spray bother them ? We have kelp available. Do we just rinse it with Fresh water and bury it under the mulch layer? Gardens alive was selling earth worm larvae – good investment? I’ll start looking for the leafminer parasitoid wasp. Thank you again for your detailed response. Dave
I think maybe I wouldn’t use the earthworm tea if you are planning to release lacewings. Nothing kills more pests than lacewings. Trick of getting them going in your yard is getting rid of ants. Ants will kill the larvae of the lacewings since the larvae of the lacewings threaten aphids. Ants love aphids and they farm them for their honeydew.
If you can control the ants, your lacewings will settle down to stay in your garden. They won’t fly away. Put the earthworm castings on the ground to kill the ants and use a handful of corn meal on top of an ant hill if you find an ants nest or ant hill. (For some reason unknown, a handful of cornmeal on top of an ants nest kills all the ants. They will be gone the next day and most time the corn meal disappears also. This is corn meal not corn starch. Some folks want to know do I mean coarse or fine corn meal? Makes no difference. Both work equally well but neither will work on an ant run, the ants will just go around. Only works when you have a swarm coming out of the ground or if you uncover a nest while working in the garden.)
As far as kelp from the beach goes, yes rinse it off, chop it up and bury it in the garden. It rots quickly. But getting it and doing all this is really hard work. I know because I’ve done it and also it wastes water. It’s better to purchase liquid and powdered kelp products and products containing kelp. Apply these according to package directions. These work well and give results sooner since they are stronger.
No point in purchasing earthworm larvae from Gardens Alive. Better, if you want to purchase an earthworm composting set and start with composting earthworms you can get here locally.
If you build up an organic soil earthworms will just naturally arrive.
Hi Pat, a couple of observations to share:
1. Lacewings from Gardens Alive arrived in a tiny container – like the one that contains salsa with your take out taco’s. Hard to believe there’s 10,000 lacewing larvae in there. They are cannibalistic so they are packed in wheat husks to provide some separation. I was wondering how to get them in the trees. Directions said use a dixie cup stapled to the tree. But, I remembered your comment about nasturciums (high pollen blooms) providing nutrition to beneficial predatory insects. I used the nasturcium blooms as cups and nested the blooms in the citrus trees.
2. the worm castings are effective directly on aphids. I found aphids feasting on a rose bud and sprinkled worm castings directly on them. Within an hour their bodies turned from green to brown and the next day they were gone. In this same rose bush I saw the ants trying to get at the lacewing larvae as you described in your book. Ants are on the retreat with all the worm casting material spread around.
Thanks again for all your great work!
Do you have any speaking engagements in the Palos Verdes area?
Dear Dave:
Thank you so much for your vivid descriptions of releasing lacewings in your garden and also for reporting back on the effects you saw of earthworm castings on ants. I applaud you for watching these miracles of nature taking place. Thank you for taking the time to report back with good results. It is a great satisfaction when we can see organic controls work and know we don’t have to resort to chemicals to control pests.
When I released lacewing larvae in my garden I first spread earthworm castings on the ground under the climbing plant where I released the larvae. The earthworm castings stopped the parade of ants that had previously been climbing up the stems of the plants. I then tied the box containing the lacewing larvae onto the plant. The eggs had not hatched but a day or two later I saw the little creatures walk safely out of the box onto the stems and foliage of the plant. They were shaped like little alligators. I used a magnifying glass but even without it I could see them. This was years ago but I still see the adult lacewings in my garden from time to time, so I know the larvae are here too.
Yes, I will be speaking this year near Palos Verdes. I will be speaking in Long Beach at the Rancho Los Alamitos on September 18, 2010 and on September 25, 2010 in Huntington Beach. Please see the schedule of events elsewhere on this website for details. I will be speaking at Rogers Gardens in Corona Del Mar on May 2 at 9:00 am.
All the best,
Pat
Pat, a few more observations to share:
1. Ladybugs – Their tendency to fly away is maddening. I learned a technique for encouraging them to stick (literally) around from my sister in law in Bellingham Wa. Pre load a spray bottle with a solution on half 7 up and half water. Spoon the ladies onto the tree and lightly spray them with the solution. The sticky sugar solution temporarily glues their wings down. In my case they were still gone in 72 hours but they probably laid some eggs while they lived in the garden – will report back if I have another generation.
2. Decolate snails – hard to tell if they are working. I may release another batch tonight since rain is expected. If I put out small containers of beer, will the deccolates also jump in, get drunk and perish?
Best regards, Dave
Dear Dave:
Thank you for your great tip on keeping ladybugs from flying away. I had never heard of spraying them with half 7-Up, half water. The sweetness might attract ants, but nonetheless it’s worth a try. My own system (See the Quick Tip on page 160 of my book) is to chill them in the refrigerator to lower their metabolism and then release them at dusk into a moist garden, placing them on low branches of plants. (They walk up, laying eggs en route.) I always figure they have been pretty bored in the container with only one pastime, thus emerge all ready to lay eggs. My results have been excellent. I always have ladybugs in my garden, but I do also grow a swathe of pollen-bearing wildflowers which gives them plenty of pollen to eat year round to tide them over when pests aren’t plentiful. I also have a fountain that runs daily on a timer and gives birds and other beneficials all the water they need. When I am out of town friends drop by my garden and keep the fountain filled.
Regarding decollate snails, it takes a year or more for them to get going since they cannot eat the large, full-grown Helix snails. You need to be catching and squashing those when you see them so they can’t continue laying eggs. Decollate snails only devour the babies. I have not released decollate snails myself because I grow so many plants from seeds (decollate snails eat seedlings), but I may change my mind and try them out. Friends of mine who own a citrus grove have had great success. They release them under boards with a small strip of wood (1/4-inch square) nailed under each end. This gives them a hiding place until they get going. Another way is to toss handfuls into thick shrubbery and undergrowth. Unfortunately, folks who have no snails usually have rats, but raccoons also eat them. Rats also eat decollate snails but since they are so small many can safely hide away. (Releasing decollate snails is illegal in some communities.)
Pat
Such great info here! The decollate snails and ladybugs I bought years ago are still around, even though my yard has had a tough few years! I released them in the evening, but otherwise didn’t do anything special, and I figured they all left. I’m so glad whenever I see them! With heavy clay soil that doesn’t drain well, the snails and slugs are especially bad in the cooler half of the year. Late this spring, I put out a healthy dose of sluggo and re-applied 2 weeks later, and then picked every one I could find in the beds (and in/under the bin I keep the hose in!). The gazanias haven’t quite forgiven me for the intrusion, but if they haven’t sprung back to their former glory by fall, I’m planning to divide & spread to other parts of the yard anyway.
But I’m thankful for the advice on this page (& this one https://www.patwelsh.com/citrus-fruit-trees/citrus-care/ ) because my lemon tree has leaf curl and leaf miners. The gardener’s “hedge” shearing (imagine an accent bush on a building corner instead of a tree) has left the foliage looking like chopped salad! I noticed a flush of new growth last week, so I asked to leave it be for awhile so I can remove some of the mangled growth behind the new leaves. The leaf miners are very easy to see in the new leaves.
I plan to try cornmeal to reduce ants in the soil nearby (I mistakenly used cornstarch & they simply dug a new entrance), and then get more earthworm castings on the ground (the castings I bought include kelp & rock dust).
It’s too late in the summer for fertilizer, I think, so I’ll worry about that in 6mos. With my dog in the yard, I need to be careful of what I use so he doesn’t get sick trying to eat it, etc. Any suggestions?
Much appreciation to you Pat & Thankful Gardener Dave 🙂
Try applying soluble gypsum once or twice a year to cure your drainage. It can do no harm and may help big time. Always put about a coffee-can full in the bottom of every planting hole. Don’t over-prune citrus! Instead, try a heavy layer of earthworm castings once or twice a year under your citrus trees to control leaf miners and leaf curl. Water and feed as usual. This will kill ants also, even better than cornmeal. Try it! Wormgold works best by the bag at many nurseries and garden supplies.
I think you could safely feed your citrus trees one more time now in early August since we have very warm weather in fall. Choose any good organic citrus fertilizer. Place under the dripline all the way around the trees and also under the canopy. Water in thoroughly. Don’t put it within 2 feet of the trunk.