–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevil populations in north central Kansas seem to be developing as expected. Fields sampled this week that had not yet been treated had greatly reduced foliage and were showing obvious signs of significant larval feeding, especially compared to fields that had been treated.
The good news is that the treated fields seem to be doing well and the untreated fields will probably only continue to be seriously impacted for about another week. Weevil populations are predominately pupae, pre-pupae, or mature larvae which should cease feeding in the next few days.
This should give the alfalfa a chance to recover. However, in untreated fields, and even fields that were treated later, after a majority of the larvae pupated, may have some adult feeding, as they may remain in fields until the 1st cutting or until temperatures start getting into the higher 80’s °F. Adults feed a little on foliage and/or may cause ‘barking’ on stems, but this usually doesn’t stress plants too much unless there are significant numbers of adults.
Very few aphids were detected, but there were a few so periodical sampling should continue to ensure that these aphid populations remain at insignificant levels.
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Soybeans seem to be growing well throughout north central Kansas. Not too many pests have been noted. However, there seem to be some spider mite populations building throughout the south central and north central parts of the state. These need to be monitored, especially if adequate moisture is not forthcoming. Mite populations can expand very quickly and really add stress to plants that are already moisture stressed.
Also, blister beetles are starting to swarm, especially in alfalfa and soybean fields. This swarming behavior is primarily for mating purposes and may involve anywhere from a few hundred to thousands of individuals. They may feed a little while swarming and actually cause plant loss, but only in small areas where the swarming occurs. Thus, treatment is rarely warranted.
By — Dr. Jeff Whitworth, Dr. Holly Schwarting
Alfalfa continues to be problematic in NC Kansas. There seems to be many fields of good alfalfa, apparently treated in an effective manner from both an insecticide and a timing standpoint, and not affected by the freezing temperatures earlier this spring. Many of these fields have been, or are being, swathed. However, there are some fields that have had, or are having, a difficult time overcoming the combination of alfalfa weevil larval feeding, early season dry conditions, and the early spring freezing temperatures. In all fields, the early season warmth sped up alfalfa weevil development and feeding, then the cooler temperatures slowed it back down. Alfalfa weevil larvae were 1st detected in NC Kansas in early March. Small, 1st instar larvae are still being detected in some fields.
Some larvae pupated and developed into adults as long as three weeks ago, and they are still in the alfalfa fields. So, NC Kansas still has a significant number of adults. Treating for adult alfalfa weevils is rarely effective, but swathing within 7-10 days should help manage both larvae and adults without an insecticide application.
Adult potato leafhoppers have also been noted in alfalfa fields. These usually migrate into Kansas between the 2nd and 3rd cuttings, so they are about a month early this year.
Wet weather has kept equipment out of the fields and has allowed the insects to flourish. Fortunately, the plants are also doing well and tolerating these healthy populations of pests. When these fields dry out and are able to be swathed, there will probably be relatively significant populations of alfalfa weevil larvae and adults still present. They are accumulated into the windrows at cutting; they will feed on the stems under the windrows until the hay is picked up. This causes the characteristic stripping in the fields where the regrowth under the windrows is chewed off while the areas beside the windrows grow back. Once the hay is removed, the adult weevils will exit the fields and no longer be a problem. Weevil larvae in north central Kansas on 7 May were 93% 3rd instar, and 7% 1st or 2nd instar. There are many pupae and adults also.
There are significant populations of aphids, mainly pea, in these central Kanas alfalfa fields as well. Swathing will remove this problem, but there are many beneficial insects helping to regulate these aphids, and hopefully they will stay around after swathing to help manage any other aphids and/or potato leafhoppers that may show up (no leafhoppers detected yet).
Some small grasshoppers were also noted. Usually, grasshoppers do better in drier conditions, but not always. So be aware that grasshoppers are present now and eggs will continue to hatch for the next month.
—Dr. Jeff Whitworth and Dr. Holly Schwarting
—by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevils continue to be very active in north central Kansas. The recent cooler weather has slowed down development a little but they are still feeding. We determined development from larvae collected on 20 and 22 April. Here is what the population breakdown looks like:
|20 AprilNo. larvae
||23 April No. larvae
So what does this mean? Alfalfa weevil larval feeding will continue for another 7-10 days, depending on the weather. Egg hatch and consequent larval feeding has been going on since 13 March in north central KS. Insecticides applied since that time have provided adequate protection, for the most part.
This photo shows KSU chemical efficacy trials with many different products being tested, and the obvious untreated plots plus the border around the plots. The rest of the field was treated with Stallion® by MKC in Abilene, KS and, as illustrated here seemed to work relatively well with 1 application. Remember, feeding will continue for at least another week and therefore treatment (or re-treatment) may still be appropriate.
Alfalfa aphids, mainly pea aphids, are becoming more numerous throughout north central Kansas. Treating for alfalfa weevils probably pretty much decimated the natural enemies/beneficials and they will not repopulate as quickly as the aphids migrate in to infest fields.