“Beneficial insects work 24 hours a day, seven days a week, and they don’t need a green card,” says Clemson University Entomologist Powell Smith.
Speaking at the recent Carolina Fruit and Vegetable Growers Expo, Smith says using what he calls ‘soft’ insecticides can provide good insect control and spare beneficial insects that can create an overall excellent insect management program in vegetable crops in the Southeast.
Beneficial insects fit into IPM (integrated pest management) programs nicely and they can help significantly with insect management. In some situations growers can get comparable insect control from a soft insecticide plus beneficials versus using a broad spectrum insecticide that kills the good and the bad insects in a field, Smith contends.
“In 2011, cabbage loopers were plentiful. Typically if we found 1 or 2 diamondback moths, we would find 8-10 loopers — it is the most unusual insect year I’ve seen in over 35 years of working with vegetable crops,” Smith says.
In tests conducted in commercial fields across South Carolina, Smith says a number of biological, or soft insecticides were used to control both diamondback moths and cabbage loopers.
The most prominent of these materials is Dipel.
Other materials include Radiant, which is similar to Spintor, which is used extensively on vegetable crops in the Southeast, as are Proclaim, Avaunt, Coragen, and Vetica. With the exception of Vetica and Coragen, all these materials come from different chemical classifications.
Having different modes of action is critical to develop a rotation program for insecticides and help reduce the risk of developing insecticide resistance. Smith says companies that sell these products have done a good job of educating growers to the active ingredient in each product.
One cabbage looper eats as much as five diamondback moths, so Smith used a threshold of one cabbage looper per 10 plants or five diamondbacks per 10 plants. Once we got to this threshold, we sprayed one of the soft insecticides, he says.
“Vegetables were planted the first week in June and by the end of the month, we had enough caterpillars to spray,” Smith says. “Each material, combined with beneficials, did a good job of protecting the crop against damage from cabbage loopers and diamond back moths.”
With Dipel, they sprayed fields an average of three times to prevent buildup to threshold levels. “With Proclaim we needed four sprays, Radiant and Coragen required three sprays. Avaunt and Vetica thresholds were reached only twice.
Application numbers good indication
“The number of applications isn’t always a good indication of the efficacy of the insecticide. Sometimes where the female lays her eggs and many other factors can affect the time required to reach threshold levels,” Smith says.
Though Dipel performed well in the tests, it has a slower potency than other materials, so it should be applied when insects are small. Otherwise, insects like cabbage loopers that can destroy a lot of tissue in a short period, can do too much damage before they finally die.
Production of brassica crops, like collards and broccoli, is up in the Southeast and continued growth is highly contingent on managing insects.
Damage from insects can have a two-fold affect on vegetable crops — it can lower actual production and in some cases not reduce yield, but cause cosmetic damage that renders the vegetable unmarketable.
Broccoli production in particular is targeted for large increases in production over the next few years. A large multi-state program that includes major universities and commercial growers in the Southeast was funded in 2011, and has the potential to bring broccoli production into vogue throughout the region.
Three primary insects that impact production of brassica crops worldwide are the diamondback moth, cabbage worm, and cabbage looper. Diamondback moths and cabbage worms came to the U.S. with the pilgrims back in the 1500s and are proof that as brassica crops move around the world, so does its pests, Smith says.
Though imported cabbage worms devastate cabbage and collard production in gardens throughout South Carolina, they are rarely a problem in commercial operations.
Over the past 10 years or so, growers in the Southeast have been attentive to adopting IPM programs and as a result we have seen fewer and fewer populations diamondback moths over the past decade, he adds.
Diamondback moths attack only plants in the family Cruciferae. Virtually all cruciferous vegetable crops are eaten, including broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip, and watercress.
Though any of these commercially produced crops are hosts for diamondback moth, collards will usually be chosen by ovipositing moths relative to cabbage and other crops.
In addition to commercial vegetable crops, a number of commonly occurring weeds are important hosts in the Southeast, especially early in the season before cultivated crops are available.
Diamondback moth can cause significant economic losses in target vegetable crops, especially broccoli and cauliflower. Plant damage is caused by larval feeding.
May disrupt head formation
Although the larvae are very small, they can be quite numerous, resulting in complete removal of foliar tissue except for the leaf veins. This is particularly damaging to seedlings, and may disrupt head formation in cabbage, broccoli, and cauliflower.
This is particularly troublesome for the Southeast’s burgeoning broccoli production. The presence of larvae in florets can result in complete rejection of produce, even if the level of plant tissue removal is insignificant.
Cabbage loopers are the largest of these three insects and they can eat a large area of foliage in a short period of time. They show up sporadically in fields in the Southeast and over the past few years have been more of ‘then’ not ‘now’ problem in commercial production, the Clemson vegetable expert says.
He says cabbage loopers are not only the largest of the three insects that cause problems in brassica crops in the Southeast, but it’s also the hardest to kill.
Cabbage loopers feed on a wide variety of cultivated plants and weeds. As its common name implies, it feeds readily on crucifers, and has been reported damaging broccoli, cabbage, cauliflower, Chinese cabbage, collards, kale, mustard, radish, rutabaga, turnips in the Southeast.
Other vegetable crops injured include beets, cantaloupe, celery, cucumbers, lima beans, lettuce, parsnip, peas, peppers, potatoes, snap beans, spinach, squash, sweet potatoes, tomatoes, and watermelons.
Additional hosts are flower crops such as chrysanthemum, hollyhock, snapdragon, and sweetpea, and field crops such as cotton and tobacco.
The high risk of damage from these insect pests, combined with their sporadic occurrence, make them ideal candidates for a combination of soft insecticides and IPM programs.
Allowing naturally occurring beneficial insects to help in controlling these pests is a win/win situation for commercial producers and home gardeners alike, Smith says.
With adequate scouting and using thresholds, vegetable growers in the Southeast can eliminate a number of sprays and still achieve good control.
It’s no longer a given that crops, like collards, have to be sprayed every week to insure a marketable crop at the end of the season, he adds.