Rainfall blessed portions of the NWP area on the last day of July; NOAA weather stations in Friona and Muleshoe recorded .5 and 1.78 inches respectively. Individual reports in excess of 3 inches were also received. The area corn crop continues to progress very well with a wide range of maturities from less than two feet tall to blister stage. The cotton crop continues to play catch up, but is developing at a good pace. Yield potential is fair to good for the most part. Grain sorghum, as with corn has a wide range of maturities ranging from vegetative to heading and blooming. Most fields are on track to fully mature but late planted fields could be hurt by frost especially if development is slowed by stress.
Corn pest pressure has increased, in addition to existing spider mite issues Southwestern corn borer (SWCB) activity has dramatically increased this week; trap captures are up 10 fold compared to last week. Yield losses from SWCB may occur as a direct result of stalk and or ear shank feeding, as well as lodging.
Bt hybrids are very effective in controlling Southwestern corn borer but required non-Bt refuge and other non-Bt corn will have to be managed traditionally. The established economic threshold for second generation Southwestern corn borer is when 20% of plants are infested with eggs or small larvae. Timing is critical when making an insecticide application; insecticides must be applied prior to larvae boring into the stalk to be effective. Small larvae will feed on leaves, ear shoots, husks, and silk for about 5 to 10 days before tunneling into the stalk or ear shank and continuing to feed. Insecticides should be selected carefully; some are harsh on beneficial arthropods and may cause a secondary outbreak of spider mites.
Spider mites persist in many fields while others remain nearly mite free. Many fields with established mite
populations have exceeded treatment threshold and have been treated. Current miticides are slower to fully suppress mites than what we see when treating most other insect pests. At 7 DAT it may look like a miticide has had no impact at the field level since there may actually be more mites present than before it was treated. In research conducted locally, labeled miticides averaged about 55% control 7 days after treatment. This is not to say that there are half as many mites in the treated plots than before treatment because mites have continued to develop, but, and it is a big but, the plots treated with miticides have reduced mite pressure compared to that observed in the untreated plots. Remember we want to minimize mite colonization of the ear leaf.
Fall armyworm have been observed feeding in non-Bt corn in varying degrees. Larvae have been observed feeding in silk, behind ears, and behind leaf collars. There is no established treatment threshold for FAW in corn but recent research confirms they can consume a significant amount of grain when feeding in the middle of the ear in addition to ear losses due to ear shank feeding. There is a detailed presentation by Pat Porter which discusses potential grain loss due to FAW feeding in corn, it can be viewed at http://goo.gl/X9jy4O
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| FAW behind ear leaf |
Cotton pests remain quiet even though I observed a “lost” bollworm feeding in a square this week. In corn growing areas, corn continues to be the favored host plant for bollworm/corn earworm at this stage. With recent precipitation plant growth should be closely monitored as we may not have enough boll load at this point to prevent excessive vegetative growth. In fields with good moisture and a later developing boll load a plant growth regulator may be necessary to keep cotton development on track.
Sunflower head moth larvae have been observed feeding in pre-bloom sunflowers which may be an indication of heavy infestations once blooming has commenced. The head moth, is the single most important sunflower pest in Texas. Sunflower moth infestations are usually heaviest early in the growing season, with another smaller moth flight possible later in the season. The adult is a small, slender, silver-to-buff gray moth about 1⁄2 inch long. It is most often seen resting on sunflower heads during the blooming period, especially in early morning and early evening. Moths are highly attracted to plants beginning to bloom. Nearly 80 percent of the eggs are laid on the plant within 4 to 7 days after buds begin to open. Eggs hatch in 24 to 72 hours. Newly hatched larvae are yellowish. Mature larvae are brown with four yellowish-green to cream colored longitudinal stripes. For the first 5 to 6 days after hatching, young larvae are relatively exposed as they feed on pollen and floral parts on the flower surface. Insecticide applications should target the very early bloom period when yellow ray petals are visible.
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| Sunflower head moth larva feeding in bud. |
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