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Insects and diseases are the scourges of summer for gardeners across North Carolina. We are beginning to see lots of insects and diseases in the landscape building up at this time.
Squash vine borers may cause a squash plant here and there to wilt, even when no other plants are suffering. Check near the base of the plant for a small hole and a mass of greenish-yellow excrement. Slitting open the stem may reveal the villain: a fat, white caterpillar. It may be possible to save the plant by removing the caterpillar, then covering the injured vine with moist soil to encourage rooting.
Aphids came out in huge numbers this year. A fairly high population can be ignored with no problem. We can’t give you a good measure of how many aphids are too many, but personal observations indicate 25 aphids per shoot on vigorous plants aren’t too many. Even if there are more than 25 aphids per shoot, natural predators will get them under control eventually.
Insecticidal soap may help control them. If you want something stronger, try one of the pyrethroids (permethrin, cyfluthrin, bifenthrin and others that end in “thrin”). You may still use some of the old organo-phosphate pesticides like malathion.
Flea beetles are common during cool weather. During a cool spring, eggplants are highly susceptible to these pests. Sevin will slow the beetles down, although warm weather that lets the eggplant outgrow the problem is the best answer for flea beetles.
This year, the Colorado potato beetles are taking a turn at eggplants. Expected hot weather should help the eggplant outgrow the problem, and handpicking the beetles is also a valid option. Sevin and Spinosad are labeled for eggplants and will help control Colorado potato beetles. Spinosad is approved for organic production.
A combination spray of pyrethrin and rotenone called “pyrellin” is showing good results in the control of many garden insects such as whiteflies, squash vine borers and various worms. It can be found under the trade name of “Bonide Rotenone-Pyrethrins Spray Concentrate” and is an organic pesticide.
It was a good year for azalea and camellia leaf gall. The galls, which are caused by fungi, don’t harm the plants, but you can prune them out to improve a shrub’s looks. This problem is sporadic. Due to the low chance this disease will occur and the minor consequences if it does, no control measures are recommended for the home landscape.
For more information, visit http://www.ces.ncsu.edu/depts/pp/notes/ornamental/odin16/odin16.htm.
The disease that shows up as orange color on the fruit of Bradford pears and crabapples is cedar quince rust. This disease lives part of the year on cedar trees and part of the year on Bradfords and crabapples. No control is possible after infection occurs, and none is really recommended for these trees. This disease is more costly when it occurs on oriental pears, but it doesn’t happen every year.
If control measures are desired on oriental pears, look for a fungicide containing mancozeb or myclobutinil that is labeled for edible fruit, and apply it before and after bloom.
Years ago, Bradford pears were considered resistant to fire blight, a bacterial disease, but that doesn’t seem to be the case now. In 2007, the fire blight was active right after the April 8 freeze event, which created cracks in the cuticle (the outer waxy layer of the stem). Some of these infections have continued growing over the years and are still causing problems. Pruning out the fire blight is helpful. See this fire blight information sheet for more information: http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/fd3.htm.
Tomato spotted wilt virus is widespread in some home gardens this year. When this disease strikes, the tomato plant stops growing. The foliage lightens up initially, and then some black discoloration becomes visible in the top of the plant. The name “spotted” comes from infections later in the season that cause spots on the tomato fruits.
After this disease strikes, infected plants probably will not produce usable tomatoes. In most years, only a small percentage of tomato plants are affected. But in some locations during certain years, the disease can be devastating. If the disease appears in June, there is still time to remove the infected plants and set out more tomatoes.