GENERAL SITUATION

Generally across the Southern Blacklands, fields are in good shape moisture wise as a result of several sets of showers that have occurred over the last month. The latest set of showers was from a cool front that blew threw early morning on April 12th, triggering thunderstorms that had wind gusts over 60 mph and over one inch of rain for most of the area. Rainfall accumulation ranged from 0.6 to 2.8 inches with the majority of folks indicating they received around 1.2 inches. The wind laid over much of the corn which has yet to establish a strong root.

CORN AND SORGHUM SOIL INSECT PESTS

Damage from soil insect pests has been very wide spread across the Southern Blacklands area this spring. Most of the damage is in fields where no at-plant soil insecticide was applied, however, even some lighter damage has been observed in fields with modest rates of standard soil insecticides. The majority of the damage that has observed is a result of the southern corn rootworm (SCR). Many growers who planted corn following cotton or wheat and did not apply an at-plant soil insecticide have found pockets in the fields where stand loss is occurring. Fortunately, this problem is only isolated in parts of fields and for the most part are not spread throughout entire fields. The common symptoms that are being observed are field of corn where stand loss is occurring or stunted plants are observed. The stand loss or stunted plants are usually in groups of two-three consecutive plants in a row followed by a group of healthy plants which is repeated throughout the heaviest infested portions of fields.

The SCR adult is better known as the spotted cucumber beetle and is greenish yellow with black spots. Adults overwinter under crop residue and along field margins and come out to feed on warm days throughout the winter. They become active in the spring and lay their eggs in the soil next to host plants. The tiny larvae burrow into the crowns and stems of corn and sorghum. Injury is especially serious to very young plants. Replanting is often necessary. In-furrow or banded insecticides applied at planting normally provide adequate control although some very early injury may occur.

Gaucho treated grain sorghum provides control of populations of SCR. Once a crop is planted without a soil insecticide, it is not possible to obtain control of SCR with a rescue treatment.

Other pests that have been observed at lower levels or in limited fields include our typical spectrum of soil pests, including wireworms, whitegrubs, and chinch bugs. Isolated cases of high populations of white grubs have been reported in a few corn and sorghum fields across the area. In addition, at least one case of a high population of grubs has been found in a coastal bermuda pasture south of Taylor where the coastal greened up in late March followed by 2/3 standloss by the April 10 due to high populations of grubs.

No reports of aphid infestations in sorghum or corn have been reported thus far. Sorghum is host to two very damaging types of aphids, greenbugs and yellow sugarcane aphids (YSA). Greenbugs are 1/16 inch long, pale green with a characteristic dark green stripe down the back. Grain sorghum, from emergence to six inches tall, should be treated when greenbug colonies are present on the majority of the plants and damage is evident. As long as growing conditions are good, producers should let natural enemies such as parasites and scymnus lady beetles control the greenbugs. Do not confuse greenbugs with corn leaf aphids that may be present in the whorl of the plant. Greenbugs are usually on the underside of the leaf.

Yellow sugarcane aphids are lemon yellow in color and are covered with small spines. They also have two double rows of dark spots down the back. The YSA inject a toxin into the plant during feeding that causes purple colored leaves in seedling sorghum and stunting and yellowing of more mature leaves. Do not confuse the redding or purpling of leaves of young plants as a result of phosphate or nutrient deficiency with YSA damage. The threshold for YSA on grain sorghum with two true leaves is 16 to 2 percent infested plants. Do not count the Cotyledon or "seed" leaves as true leaves. Once an entire true leaf is discolored, damage to the plant is significant.

COTTON INSECTS

Cotton currently ranges from still in the bag to the 1-2 true leaf stage with the majority at the cotyledon stage. Somewhere around 80 percent of the cotton has been planted across the Southern Blacklands. For the most part, that which has emerged has come up to a good stand. There are isolated cases where it appears that poor seed has resulted in a bad stand. Most of the cotton has just emerged and therefore, insect pests such as thrips and aphids have not had time to locate the fields, but just give them a couple of weeks. For the most part, growers use modest amounts of soil insecticides that will protect their cotton stand at least through the 1-2 true leaf stage. Protection beyond this stage will be dependant on the product and rate used.

As previously mentioned, thrips are one of the early season pests of cotton. Thrips are narrow, straw-colored insects about 1/15 inch long. They often infest the small, folded leaves in and around the terminal of the cotton plant and may attack young leave, leaf buds, and very small squares. Thrips damage can cause a silvering of the lower leaf surface, deformed or blackened leaves, terminal loss, and square loss. Thrips damage often causes the leaves of cotton to curl up or cup. If cool, wet conditions persist in fields, heavy thrips pressure can result in delayed fruiting and crop maturity. Control for thrips may be justified when the average number of thrips counted per plant is equal to the number of true leaves present a the time of inspection. Insecticidal control is rarely justified once plants have reached the 7 true leaf stage.

Another type of insect that normally infests young cotton is aphids. The two most common species of aphids that are commonly found in cotton across the Southern Blackland are cotton aphids and black cowpea aphids. Cotton aphids range from light yellow to dark green to almost black. The immature or nymphal stage looks like the adult stage, only smaller. Most adults do not have wings. Cowpea aphids are shiny black with white patches on the legs and are common on seedling plants. Aphids are usually found on the underside of leaves, on stems, and in the terminals of the cotton plant. Heavy and prolonged infestations can cause leaves to curl downward and the older leaves to turn yellow and shed. Natural control by weather, predators, parasites, and pathogens can be effective in holding populations below damaging levels. Aphid population abundance can rise and decline for no apparent reason. Insecticidal control should be delayed until infestations exceed 50 aphids per leaf and have been sustained for at least a week.