I love gardening, and I love talking about gardening. But I want this blog to be helpful to its readers, so I thought I might start sharing some of the great questions I have been asked. If one person has an issue, it’s likely several do, since some of our major gardening issues are triggered by weather and insect life cycles that we all share.
I got a great question last summer about some common damage to pecan leaves. This type of damage will begin showing up soon, so this information should help you get ahead of it. The question was: Help! Something is eating my pecan leaves. What do I do?
Insect damage without the insect present is always a challenge. It requires a bit of sleuthing. The clues I asked her to gather were:
• What does the damage look like? Are there holes eaten through the middle of the leaves, or are the margins (edges) eaten? Do the holes go all the way through all parts of the leaf or are they skeletonizing the leaves (leaving the veins and ribs)?
• Is there any webbing present?
• Is there any frass (insect droppings) evident?
These were the likely suspects:
• Sawfly – Leaves eaten in early spring by light-green caterpillar. Midribs and veins of leaves left intact (skeletonizing)
• May Beetles – Brown beetles feeding on foliage at night
• Green June Beetles – Green beetles feeding on foliage at night
• Walnut Caterpillar – Large colonies of black caterpillars with long, soft hairs feeding in colonies on foliage; no webs
• Pecan Catocola · Dark gray, active caterpillars up to 3 inches long feeding on foliage in early spring
After I got her response, which was accompanied by a photo of the damage, we worked with a process of elimination. We excluded the Pecan Catocola because at 3″ long and active in a colony she would have seen the insect, and she hadn’t. The sawfly was eliminated next because entire sections of the leaves, including the mid-veins and part of the mid-rib, were being devoured, not skeletonized.
That left the Walnut Caterpillar and the two beetles. The treatment for each was different – BT for the caterpillar, and Spinosad for the beetle – so we had to narrow it down further. The Walnut Caterpillar has an interesting feeding pattern. A group hatches, feeds together for a few days, then goes down to the bark to shed their skins (molt) and begin their next stage (instar). They repeat this through their development stages, and do the most leaf damage in their last few stages. After they finish feeding, they drop to the ground and pupate in the soil. There will be at least two generations a year, and the second generation causes more damage than the first. To make a certain ID on them, we would have had to wait until she caught a group out in a feeding stage.
The only way to eliminate the beetles and zero in on the Walnut Caterpillar was for her to go out at night to see if she could get eyes on the beetles since they are both night feeders. Sure enough, she and her husband went out about 10:00 pm one evening, and observed quite a few small brown beetles feeding on the leaves. Since May Beetles are a smaller version of our common brown June Beetle, we had our ID.
She had several treatment options:
• Do nothing – it’s pretty much just aesthetic damage and unlikely to affect nut production
• Use Spinosad – a relatively broad-based insecticide with lower toxicity to beneficial insects when used according to label instructions
• Bait & trap – a non-toxic option that also decreases the numbers of overwintering grubs
She opted for a combination of a one-time application of Spinosad followed by Bait & Trap all summer. This method works for several summer pests that are active at night and can decrease their numbers quite effectively if used for several seasons.
Bait & Trap for Beetle Pests
• Fill a bucket, pail, or washtub with water leaving several inches to the rim.
• Add 1 tsp of liquid dish soap per gallon of water.
• Place the bucket in the garden close to the affected plant.
• Drive a light-weight t-post into the ground beside it.
• Attach a clamp light to the post about 10” – 12” above the water. (I strongly recommend that you secure the clamp light with an additional zip tie so there is no danger that it will fall into the bucket).
Let the light shine at night. Many bugs will be attracted to it and fall into the water. Dump the dead bugs out in the morning. If you want to use the trap for several nights scoop them off the surface with a net or sieve and discard them in the compost or trash.
If you have a pet that might have access to the bucket, place a ring of wire around it so they are not tempted to drink from it.
If you see similar damage on your pecan trees this summer, maybe this blog will help you do your own sleuthing and make your treatment decisions. You can always gather the clues and take them and a leaf sample to your Arbor Gate nursery professional for confirmation and assistance in selecting the treatments and equipment you need to treat safely. If you have any questions about this blog, or have a question you think would be useful here, email me at [email protected].