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Pre-Season Vegetable Pest Forecast for 2018

Forecasting pests can be tricky. While conditions that favor or curb various insects or diseases can give plant pathologists and entomologists an educated guess on what will and won’t be a problem, those indicators are no guarantee that the season will unfold as anticipated.

“Predicting which insects may or may not be a problem is very tricky, and anybody’s guess,” says Alton “Stormy” Sparks from University of Georgia.

hat said, we reached out to experts across the country to give their best guesses about how the spring 2018 season will look like, pest wise.

Southeast: Whiteflies and White Mold

Anthony P. (Tony) Keinath, Vegetable Pathologist, Clemson University: White mold is widespread in South Carolina on winter vegetable crops. Even if vegetable growers have lost overwintered vegetables to cold injury or white mold, spring-planted cool-season vegetables will also be at risk from white mold. Diseased crops should be destroyed immediately by disking or plowing to prevent sclerotia from forming.

Soil temperatures here at the Clemson Coastal Research and Education Center remained above freezing during our snowstorm on Jan. 3 to Jan. 7. Average soil temperature 2 inches deep for the period was 35.1?F, with a maximum of 36.1?F and a minimum of 33.5?F.

The only disease that may have been reduced by the low soil temperatures is southern blight, as the fungus (Athelia rolfsii) is sensitive to freezing temperatures, and our temperatures were close.

Growers in the Southeast should be on the lookout for white mold; I already saw some on my snapdragons in the past two weeks. Cold temperatures break the dormancy of sclerotia of the white mold fungus (Sclerotinia sclerotiorum), triggering those close to or on the soil surface (or on crop debris) to form tiny mushrooms that eject ascospores in the air. If the ascospores land on cold-damaged tissue of vegetables like kale or parsley that growers may be overwintering, the spores will germinate readily, colonize the injured parts, and then spread to healthy tissue.

The most effective fungicides are those in FRAC Group 7 (active ingredients boscalid, penthiopyrad, or fluxapyroxad). The challenge with this group of fungicides is that only two applications are allowed. Growers should make one application now, then another in 4 weeks, or sooner if white mold symptoms are seen on the farm.

Organic growers can apply Contans (Bayer Crop Science), a commercial product that contains the biocontrol fungus Coniothyrium minitans. This product works best applied several months before sclerotia germinate, although it also has worked in some trials when applied at transplanting. Organic growers who plan to grow lettuce or beans this spring should apply Contans now.

Stormy Sparks, Entomologist, University of Georgia: In general we expect insects that overwinter in this area, and are not in some protective habitat or diapause, to be impacted by cold weather.

Insects I hope are being affected include whitefly, pepper weevil, and squash bug.

Whitefly and pepper weevil were severe last fall, and both remain active during the winter. We assume, and hope, that the weather we are experiencing will reduce them to normal populations for the spring.

Cold winters can also affect other insects, like thrips; however, much also depends on what happens after the cold spells. If we suddenly warm up and have a warm spring, many insects can rebound rapidly.

Bottom line: We anticipate that the weather we have experienced thus far should help us greatly with certain pests (whiteflies and pepper weevil), but that same weather could have minimal impact on other pests.


Bernard H. Zandstra, Dept. of Horticulture, Michigan State University: My experience is that weeds survive soft or hard winters. If spring comes early, which has been the common occurrence in recent years, we can expect to see the common spring weeds: henbit, purple deadnettle, white campion, yellow rocket, shepherdspurse, common chickweed, curly dock, horseweed, dandelion, wild carrot, and others. Aggressive activity to kill emerged weeds before working the soil will improve weed control during the season. One or two quarts of glyphosate in early spring will kill many over-wintering and germinating weeds.

If spring comes later, these weeds along with the annual grasses, quackgrass, and later-germinating weeds will all appear about the same time.

Ricardo Bessin, University of Kentucky: In December, our freezing temperatures froze the ground several inches deep. This will impact overwintering of corn earworm in the area. For producers, they would get some relief until the migrating populations arrive from the south. I would also expect some reduction in thrips.

Daniel S. Egel, Extension Plant Pathologist, Southwest Purdue Agriculture Center: Here in the Midwest, I do not expect any impact from the cold on any pests of any kind. Thus, I have no foreshadowing of which pests might be important next year.

West/ Southwest

Vonny M. Barlow, Entomologist, University of California, Davis: Typically the insects that we must watch out for in vegetables are aphids, thrips and whiteflies.  You are correct that mild winters will have less of an impact on overwintering insect populations. It is too early at this point to predict what insects will be a problem. Much of our ground is being worked now for soon to be planted broccoli. After that, melons and corn. Corn traditionally have corn earworm issues and they are seasonal depending on the adult moth populations that come into the area.  I know this is not a firm answer but it is the best answer available at this time.  Everything else would be guess work.

John C. Palumbo, University of Arizona: Our weather in Arizona and Southern California has been the opposite of the Southeast. We have been dry (has only rained abount a 0.10 inch since September) and unusually warm (5 to 10 degrees above normal all winter; no freeze events in most areas). Consequently, these conditions are conducive for 1. Western flower thrips, which we expect to be heavy on spring leafy vegetable crops, and 2. Whiteflies, which we expect will be heavy in our spring melons. Pest pressure for both insects is positively influenced by the lack of cold weather and rainfall.

Richard Smith, Vegetable Crops and Weed Science Farm Advisor, University of California Cooperative Extension: It is a bit too soon to tell for our area. However, thus far it has been a dry and mild winter. We don’t have an entomologist or pathologist right now, so no one to lean on regarding those pests for this area.


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