Northwest Plains Pest Management News Vol XI Issue 9

Crops have progressed very well this past week, what a difference a rain makes! The area corn crop ranges from 4 leaf to blister stage and even though some fields have taken a beating from mother nature it looks good on a whole. Much of the area cotton crop is finally blooming; nodes above white flower (NAWF) have ranged from 6-9 indicating good yield potential, time permitting. The crop is about two weeks later than what we would like to see, but currently most fields are progressing at a high pace. The reduced effective bloom period will likely limit top end yield but August and September weather conditions will determine to what extent.  Cotton will need to be carefully managed to promote earliness to preserve as much yield potential and fiber quality as possible. Area sorghum is also rapidly growing but, as with cotton, later planted fields are in a race with mother nature to mature before frost.

Spider mites must not have read the text book as they did not seem to slow a bit during recent cooler and more humid conditions. Many field have exceeded treatment thresholds and many more are near it. Even small mite colonies have a tremendous number of eggs indicating the potential for continued rapid population expansion. Treatment threshold at this point can be simplified to an established mite population in the lower 1/3 of the plant with small colonies beginning to develop near the ear leaf with end goal preventing colony establishment on the ear leaf. As I mentioned last week population dynamics are extremely important in managing spider mites, regular field evaluations should be made to document population trends and natural enemy activity.  A rapidly developing mite population should be dealt with more aggressively while a slower developing population may allow some flexibility to determine if natural enemies will keep them in check. We have several trials out evaluating different products and rates, hopefully they will provide information that will help make good pest management decisions.

Banks grass mites and eggs

Weeds continue to be problematic and difficult to control. Control problems can be attributed to several reasons and in many cases combinations of factors including environmental conditions, weed size and condition, herbicide coverage, weed resistance to herbicides. As weed management decisions are made consider all management options and don’t automatically rule out “low tech” tactics such as cultivation and hand hoeing. To my knowledge no weed has developed resistance to the separation of above ground parts from below ground roots. If weed resistance is suspected deal with it aggressively, make every effort to prevent the loss of herbicide efficacy due to resistance.

Southwestern corn borer (SWCB) field level infestations have been reported even though moth captures in traps have remained relatively low with slight increases recently. The changing agriculture landscape including  planting use of Bt hybrids, as well as previous years use of Bt technology may be making trapping less effective in predicting area wide potential pest activity. Populations of SWCB appear to be much more localized and more difficult to predict than the more uniform infestations of yester year. The established action threshold for SWCB is met when 20% of plants are infested with eggs or small larvae. Most eggs will be laid on the middle 7 leaves; the ear leaf, 2 above and 4 below.

Hatched SWCB eggs

As cotton transitions into the early bloom stage we no longer consider cotton fleahopper a risk but we need to continue monitoring cotton for significant Lygus infestations. During the early bloom period the action threshold for Lygus is 15/100 sweeps (4/beat sheet sample) with unacceptable fruit shed. Current Lygus infestation levels remain low. Fields adjacent to weedy areas should be closely monitored when the weeds are destroyed as Lygus will migrate into cotton.

Lygus Adult