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Soil insecticides boost pumpkins

Soil insecticides boost pumpkins

Clemson University researchers are looking at the efficacy of injecting insecticides under a pumpkin crop in irrigation water.

Controlling aphids, whiteflies and a number of other sucking pests that can be a major threat to pumpkin production is an ongoing challenge for growers who produce the one-shot, niche crop for Halloween.

Soil injected neonicotinoid insecticides can be an efficient way to get early season control of these pests. The problem has been getting the right amount of material to the plant’s root system. Researchers at Clemson University’s Edisto Agricultural Research and Extension Center in Blackville, S.C. are using a Dosatron to apply Admire, a neonicotinoid insecticide to the root system of pumpkins planted on plastic mulch.

Whiteflies, in particular, can be a double-threat to pumpkin and other cucurbit production, because these pests cause direct damage to the fruit and can vector other harmful viral diseases.

Whitefly adults congregate, feed, and mate on the under-surface of the leaves of the host plant and can occur in high enough populations to create white cloud-like materials when the insects are disturbed.

Direct crop damage occurs when whiteflies feed in plant phloem, remove plant sap and reduce plant vigor. With high populations plants may die. Whiteflies also excrete honeydew, which promotes sooty mold that interferes with photosynthesis and may lower harvest quality.

Plant disorders and virus transmission are of particular concern because they can occur even when a whitefly population is small. In general, the older the plant when infected with virus or the later the onset of plant disorders, the less damage to the crop, so preventative action is critical.

Not only can these tiny insects be deadly in small numbers, they are even more of a threat because they are known to attack over 500 species, representing 74 plant families. With pumpkins, which are typically planted in mid-summer and harvested prior to Halloween, many of these host plants are gone, leaving fewer options for whiteflies to attack.

Speaking at a recent field day at the Edisto Station, Extension pest management specialist Powell Smith showed more than 100 farmers in attendance the irrigation system rigged to inject Admire to control these pests.


Effective materials

Neonicotinoids have been on the market for nearly 10 years and have been highly successful in managing aphids and white flies on a number of vegetable crops. The only negative, according to Smith, is that this family of insecticides has been linked to bee problems. He stresses the jury is still out on the amount of bee damage caused by these materials.

Clemson horticulturist Gilbert Miller, who is conducting the pumpkin tests, says he has two bee colonies near the test plot and has seen no problems with using Admire. The jury is still out on whether this family of chemistry causes or helps cause collapse of a bee colony, he adds.

Neonicotinoids get into the plant tissue and circulate through the plant. They don’t get into the fruit and flower of the plant, so they are very fruit friendly.

These materials work best when they are absorbed by the root system of the plant. In the Clemson tests, conducted at the Edisto Agricultural Research and Extension Center in Blackville, S.C., Miller mixed up the proper amount of insecticide to cover the test plot acreage, and used a proportional injector to inject the material into irrigation water.

The proportional injectors, in the Edisto tests are based on the proportion of water that passes through them. The system sucks out the correct proportion of pesticide intended for the field.

Dosatron injectors work using volumetric proportioning, ensuring chemical mixtures, in the Clemson pumpkin test, Admire insecticide, remain the same, regardless of variations in pressure and flow. When water enters the injector, it triggers the hydraulic motor, which begins moving up and down inside the body of the injector. On the up stroke, the Dosatron draws fluid up from the concentrate tank in an action similar to a hypodermic syringe


Same family

Admire is one of several insecticides currently on the market that are in the same neonicotonoid family. Like many insecticides, neonicotinoids have shown a tendency to develop resistance problems when used too frequently. Smith stresses that a number of neonicotinoid insecticides can be used instead of Admire, but these materials should not be used in conjunction with it.

The injection rate of Admire is based on the number of linear (row) feet per acre. Row spacing is critical in figuring the proper amount of the pesticide to use. A three-foot row spacing, for example, will have about 15,000 row feet per acre. A six-foot row spacing, by comparison, has about 7,200 row feet per acre.

“It is very important to remember to not follow up an injection of a neonicotinoid with a foliar application from the same family. If you get white flies in a field that has been treated with injected Admire, or a similar neonicotinoid insecticide, you could be setting yourself up for resistance problems by coming back later in the season with a foliar application of the same family of materials,” Smith says.

He also says that injecting a neonicotinoid immediately after planting isn’t a good idea, because the plant’s root system isn’t developed enough to absorb the insecticide. A better bet is to wait 7-10 days after the transplants are set before injecting Admire, or any other neonicotinoid.

The test plot of pumpkins at the Edisto Station was planted July 1 and Admire was injected on July 8. Under plastic, with good moisture and high temperatures the root systems will develop quickly and should be able to absorb most of the injected pesticide, Smith says.

By waiting, the plants develop a better root system and they will make better use of the injected materials. By waiting, the grower will also get better use of his crop protection dollars, Smith explains.

Miller notes the pumpkins used in the irrigation study are genetically modified, with resistance to the four major viruses that attack pumpkins. He encourages growers to attend Edisto’s fall field day at which time the genetically altered pumpkins will be discussed further.


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