–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevil feeding activity has slowed significantly in north central Kansas, at least south of I-70. North of I-70, larvae are still developing and thus feeding, but even in the northern counties this feeding and resultant damage should be significantly reduced by the end of the next week. There are still some small larvae but the majority of populations are pupating or have pupated. Adult weevils are still hanging out in alfalfa fields and probably will until that 1st cutting, or temperatures get into the mid-80’s or warmer.
–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing
Alfalfa weevil larvae continue to hatch throughout north central Kansas. Plants still do not seem to be growing very much. The larvae that have hatched are still tucked inside the tightly closed terminals where they do not shake out very readily when utilizing the “shake bucket” sampling technique. Thus, many producers are underestimating infestation levels. So, when sampling to determine treatment threshold, be careful to account for the small stems that hold larvae which aren’t shaking loose. These small plants need to be totally pulled apart to get an accurate count on alfalfa weevil larvae.
22 March, 2017 – Showing little growth in alfalfa
As of 22 March, there were various developmental stages of larvae. Pea aphids were still present in all alfalfa fields that we checked. However, no infestation level that would be of concern was detected. Also some producers have/are burning the existing alfalfa as a form of weevil and weed control.
Picture of an apparatus for burning provided by “The Specimen”
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa in north central Kansas doesn’t seem to be in the overwintering mode yet. It is still growing, albeit slowly. But, the unusual situation this warmer-than-average fall weather has caused is with alfalfa weevils. On 16 November, several alfalfa fields were sampled in north central KS and many adult alfalfa weevils were captured. However, the unique situation was the sampling of many alfalfa weevil larvae. Some leaf feeding by these larvae was also evident. These insects are normally univoltine (one generation of alfalfa weevils/year). The adults are moving, or have moved, back into the alfalfa fields by now and started laying eggs. Eggs laid in the fall are not normally developed enough to hatch this time of year. Late February is usually the earliest that alfalfa weevil eggs hatch. After the coming cold front moves through and temperatures warm back up we will re-sample to determine how the cold temperatures impacted these larvae.
Also, there are many pea aphids present which is not as unusual for this time of year. Numerous lady beetles are also present but they do not seem to be feeding on either pea aphids or alfalfa weevil larvae.
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.
–by Dr. Jeff Whitworth, Dr. Holly Schwarting & J.R. Ewing
Cool, wet weather continues to dominate the state. This has allowed the alfalfa weevil adults to remain in the alfalfa fields. As they remain in fields they are feeding in/on terminals and the new foliage. However, they don’t feed anywhere near as much as the larvae, plus there aren’t near as many so, the feeding really is negligible. However, they do cause concern and their feeding on the new foliage and “barking” of the stems can slow regrowth if they remain in fields. Swathing alone will not eliminate the adults if the weather continues to be only in the 80’s for daytime highs.
The first potato leafhoppers of the summer were detected in north central Kansas on 19 May. This is a little earlier than usual but fits right in with the unusualness of this spring.
Pea aphid populations have been steadily increasing the past couple of weeks. However, sampling some of the same alfalfa fields on 19 May indicated the aphid populations have reduced relatively dramatically. There are many larval and adult lady beetles in these fields and they can even be readily observed feeding on the aphids. So, these beneficials really seem to be helping with aphid control.
—Dr. Jeff Whitworth – Dr. Holly Schwarting – J.R. Ewing and Salehe Abbar
Alfalfa weevil feeding is winding down in north central Kansas, but not as fast as usual. If treatment is still considered prior to swathing do not forget to read the label and follow the PHI (post-harvest interval) required by the product you choose. The untreated control plots in our insecticide efficacy trials are still above our treatment threshold of 1 larva/2 stems, or 50% infestation, and contain many small larvae. Remember, larvae were 1st detected on 13 March so they have been actively feeding for six weeks. However, the good news is many insecticides are still providing excellent protection from one application three weeks ago. See below:
Aphids continue to increase in alfalfa fields. They are primarily pea aphids with a few spotted aphids. Have not seen or heard of any at, or even close to, treatment thresholds, but populations are increasing. Lady beetle and parasitic wasp populations seem to be rebounding which should help slow down these aphid populations.
—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.