Volume XXVII No. 10 May 29, 2002 GENERAL SITUATION: A little drought relief blessed the LRGV this past Friday night and Saturday morning. Rain amounts were very spotty, ranging from 0 to 4 inches. Nearly everyone received a little rain, but few received in excess of 0.75 inches. Cooler day time temperatures resulting from the cool front that precipitated the moisture led to some positive growth in irrigated cotton and sorghum fields and a hand full of dryland fields. Insect activity remained very light overall this week. Cotton was blooming in most fields and some of the earlier planted fields ( late February and early March) had many bolls present in irrigated blocks. Heavy fruiting this week was putting a strain on field water supplies. Irrigations were ongoing if water was available to growers this week. Some irrigation districts were anticipating running out of water this week and no additional rain was in sight to change those conditions. Bollworm/tobacco budworm activity was much reduced this week compared to last week. Tobacco budworms were the primary pest in one field near La Feria based on field identification late last Friday. Most other larvae that were checked on Monday of this week appeared to be primarily bollworm. Counts of eggs ranged from 0 to 3 per 100 plants this week and worms ranged form 0 to 2 per 100 plants. Worm counts could change again in the next 2 to 3 weeks. Fields which have had good growth response to either irrigation or rainfall, should be checked frequently. Both worms and boll weevils tend to survive at higher levels when field conditions are moist and relatively cooler temperatures prevail, like at the present time. Another cycle of worms could occur within the next1 to 2 weeks if the oldest larvae seen late last week and early this week are an indication of the age of the recent bollworm/budworm population. Be alert. Boll weevil punctured square counts were not reported to us this week. However, the weekend's weather system made field conditions more favorable for weevils. Since we had reports of some weevil activity last week, there should be no reason not to expect a slow down in activity this week. Weevils are probably sneeking around in somebody's fields somewhere, right now. Cotton aphids were some lower in numbers this week than last week. Overall, aphids were not as serious this season as was anticipated. They continued to be a potential threat in a few fields where counts exceeded 100 per leaf.

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PEST CAST continued

Sorghum in irrigated fields looked in excellent condition this week. No reports of aphids were received this week. However, we have some reports of greenbug aphids in the Coastal Bend this week. Following what was a heavy cornleaf aphid infestation in many area fields in the LRGV the last couple of weeks, beneficial insects increased to large numbers and have been moving around, even into cotton. If greenbugs appear, we should expect to have some help from beneficials which were reared on cornleaf aphids. But, watch for greenbugs and make certain that they are not being controlled by beneficials before making any insecticide applications.

Dr. Roy Parker, Extension Entomologist at Corpus Christi, made the following report on greenbugs in their weekly insect newsletter Insects and Weeds in Focus, which we thought was a timely and excellent article on managing greenbugs in sorghum:

SORGHUM INSECT WATCH

It is apparent that greenbugs are increasing in sorghum at various locations in Coastal Bend counties at the same time corn leaf aphids are declining. The predators (lady beetles, lacewing larvae, pirate bugs, spiders, etc.) and parasitic wasps which increased in number on corn leaf aphids are present in high numbers. These natural enemies are expected to bring greenbug numbers down rapidly in most fields. However, there may be situations where control measures would be appropriate.

Greenbugs feed in colonies on the underside of leaves. Infestations may be detected by appearance of reddish top surface leaf spots which is caused by the toxin infected by greenbugs. Damage leaves begin to die, turning yellow then brown.

Larger sorghum plants tolerate more greenbugs. Yield reductions during boot, flowering and grain-development stages depend on greenbug numbers, length of time greebugs have infested the plants, and general plant health. Many greenbugs on booting and older plants can reduce yields and weaken plants that may later lodge.

When deciding whether to control greenbugs, consider the amount of leaf damage, number of greenbugs per plant, percentage of parasitized greenbugs (mummies), numbers of greenbug predators (lady beetles) per plant, moisture conditions, plant size, stage of plant growth and overall conditions of the crop. It is important to know from week

to week whether greenbug numbers are increasing or decreasing. For example, insecticide treatment would not be justified if the recommended treatment level (based on leaf damage) had been reached but greenbug numbers had declined substantially from previous observations.

Plants can tolerate about 30 percent leaf loss before yield is reduced. Greenbug infestations after sorghum flowering and before the hard-dough stage should be controlled before they kill more than two normal-sized leaves on 20 percent of the plants.

Insecticides include Furadan 4F (state 24C label), Lorsban, dimethoate, Disyston, malathion, and ethyl parathion.

Begin now to think about sorghum midge control, especially in fields that will reach the bloom stage 3 or more weeks after older sorghum began to bloom. Scouting fields for sorghum midge on a daily basis and determining the extent of field area infested is time consuming and labor intensive, but close attention can pay big dividends in money saved and crop protected.

I would suggest you contact us for a copy of Extension publication B-1220 dated June 1998, titled "Managing Insects and Mites on Texas Sorghum" and read carefully information dealing with the greenbug and the sorghum midge. RDP

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