The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released Feb. 21, 2012.

Western flower thrips in spring produce crops

By John Palumbo, UA Research Scientist and Extension Specialist

Western flower thrips are beginning to increase throughout the Yuma County, Ariz. area. The thrips have slowly been increasing in the Yuma Valley, but reports from the Dome Valley area suggest they are occurring in much higher numbers there.

With the light rain experienced last week, we would not anticipate any significant reduction in numbers like we usually see in wet springs. Typically, heavy rainfall will dislodge or even drown adult thrips on plants, and can suffocate larvae in the soil if it remains wet for prolonged periods.

Historically in dry, warm winters like this season, thrips numbers have been found much higher at this point in time. That has not been the situation to date and we are not quite sure why.

However, another factor pest control advisers should be concerned with this time of the year is thrips "bioconcentration" which occurs each year in late February and March as lettuce acreage declines.

Each time a lettuce field is harvested and disked adult thrips populations disperse from these areas into the next available lettuce field. This is generally coincident with higher temperatures suitable for thrips development.

As the number of lettuce acres becomes reduced near the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production.

This can often make chemical control very difficult, particularly in March, as thrips adults may continually re-infest fields following spray applications.

Research note: Under current population pressures, Radiant (7 oz/ac) and Lannate (0.75 lb) + pyrethroid (high rate) are providing good residual efficacy of thrips in our trials at the Yuma Ag Center. The key to preventing thrips from significant scarring leafy vegetable plants is to prevent immature populations from becoming established.

For more information on the identification, biology, ecology, and management of thrips on desert produce, visit these links: Thrips Management in Desert Leafy Vegetables - 2012 and Insect Management: Western Flower Thrips.

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Late blight of celery

By Mike Matheron, UA Extension Plant Pathologist

Late blight of celery, also known as Septoria blight, is one of the major diseases on this crop worldwide.

The causal pathogen is the fungus Septoria apiicola. Periods of wet weather that favor disease development can result in significant yield and quality losses when the pathogen is present.

The disease can occur in Arizona celery fields. However, the generally dry environment in this region restricts rapid and widespread disease development.

Disease symptoms on leaves begin as irregularly shaped spots that are initially yellow and then turn necrotic and coalesce causing leaf blight. Infections also occur on the stalk.

Small spore-producing fungal bodies called pycnidia appear in the necrotic tissue on leaves and stalks. Pycnidia are similar in color and size to ground pepper grains. Each pycnidium can produce from 1,500 spores to 4,000 spores.

The usual sources of initial inoculum in many celery production regions include infested seed and over-seasoning celery debris. However, in desert production areas, crop debris rapidly decomposes and is not likely a factor in disease initiation. Since seeds are an important source of inoculum, planting pathogen-free seeds is a crucial disease management decision.

However, even so-called pathogen-free seed lots may contain a very low level of infested seed which can in turn lead to occasional infected plants.

If fungicide application is necessary, compounds including azoxystrobin, chlorothalonil, copper hydroxide, propiconazole, pyraclostrobin, and trifloxystrobin can be effective disease management tools.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Nutsedge identification

By Barry Tickes, UA Area Agriculture Agent

Identification is an important first step in weed management. Nutsedge is a difficult to control perennial weed throughout Arizona.

There are two species of this weed that cause problems here and are often misunderstood.

Although it is often called nutgrass, nutsedge is neither a nut nor a grass. It is instead a member of the sedge family.

Unlike grasses, sedges have solid triangular stems. Grasses commonly have round, flat, or oval stems that are hollow. Sedge leaves are thick and stiff with a distinct midrib and are arranged in sets of three at the base.

Although there are many sedges, only two are weeds here and these are among the most damaging and difficult to control. These are purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus).

Both are perennial weeds that are dormant during the winter. Each produces seed although the seed is rarely viable and spread vegetatively by below ground tubers (nutlets). These tubers are produced on rhizomes or below ground stems. Most of these tubers are within the top foot and a half although they can be found much deeper.

Each tuber has up to seven buds from which new rhizomes and tubers grow. When shoots reach the surface they form basal bulbs and new leaves to keep this process fueled. In a single season, one tuber can produce almost 2,000 new plants and 7,000 new tubers.

These tubers can persist for several years and must be depleted to achieve complete control.

Purple and yellow nutsedge respond differently to herbicides and it is important to make proper identification. Mixed populations can be found here and yellow nutsedge is, in general, easier to control.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

Presentation on Shepherd’s purse

Presenter: Kaylee Renick, PLS 300 Weed Science Class , "Shepherd's Purse: Capsella Bursa Pastoris L."

Click here to: WATCH VIDEO