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Extension Entomology

Tag: freeze

Alfalfa

–by Dr. Jeff Whitworth

Much of the alfalfa throughout north central Kansas was significantly affected by last week’s freezing temperatures, as previously noted. This is especially true of older, less robust stands, as indicated by the plants in the lower left portion of fig.1. Sampling these freeze-affected

Figure 1 Alfalfa affected by the freeze (by Cayden Wyckoff)

areas with a sweep net revealed only very few live alfalfa weevil larvae, i.e. an average of 1 live larvae/10 sweeps. However, the less freeze-affected plants (upper right portion of fig. 1) had a much more significant infestation, i.e. these areas averaged 26 live larvae/10 sweeps. The vast majority of alfalfa weevil larvae detected this week were mature larvae, and many were actually on the ground, see Fig. 2. probably preparing to pupate, as a few new adults were also detected, again, see Fig 2.

Figure 2 Mature Alfalfa weevil larvae, new adult AW plus aphids and Lady beetle larva (by Cayden Wyckoff)

Figure 3 Aphids and lady beetle larvae (by Cayden Wyckoff)

 

Aphid populations, both pea, see Fig. 3, and cowpea, seemed to have dramatically declined also. This is probably a combination of the freezing temperatures coupled with a healthy population of lady beetle larvae, see Fig. 3, which have been voracious feeders on these aphids.

 

Alfalfa Weevil Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still very active throughout north central Kansas.  They also range in development from small 1st instar larvae to relatively mature 3rd instars.

Aw life stages

We have also had reports of pupae in south central and north central Kansas.  Many fields are still showing signs of freeze damage.

freeze damaged field

The freeze did seem to affect the weevils by slowing their development but did not kill them.  However, most larvae in freeze-damaged fields are more yellow than the usual greenish color.  Whether that means they are getting the proper nourishment from the yellowed, freeze-damaged alfalfa tissue or not is unknown.

larvae color difference

Weevil larvae in untreated, non-freeze-damaged fields seem mostly about to pupate within 7-10 days if temperatures stay between 45-80°F.  No other pests have been noted in alfalfa fields we visited over the past week.

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