Home Crop Monitoring Alfalfa weevil hitting early cut hay stands hard

Alfalfa weevil hitting early cut hay stands hard


A number of reviews of poor regrowth on second- or later-year alfalfa within the Niagara and different Ontario areas appears to be attributable to one perpetrator: alfalfa weevil.

Agronomists are reporting scouting fields which have already reached threshold for the pest (see photographs beneath). Due to early season warmth, some established fields of alfalfa had been cut comparatively early this 12 months and had been gradual to regrow. Scouting these poor fields revealed alfalfa weevil because the perpetrator.

As to why the weevil is having such a devastating influence already, resident RealAgriculture agronomist Peter Johnson says that gentle winters can improve grownup survival, as they reside in crop particles. In a extra typical 12 months, dry situations improve ranges of useful pathogens to maintain numbers in examine, nonetheless the chilly April and Could temperatures could have slowed improvement of the pest, and adults emerged a bit later.

Weevil injury on second cut alfalfa, early June. Ryan Benjamins, 2021

This 12 months’s sooner than regular hay harvest as a consequence of dry climate and superior grass stage, implies that numerous alfalfa was harvested earlier than bud which is usually peak larval assault, Johnson says.

Tracey Baute, area crop entomologist with the Ontario Ministry of Agriculture, Meals and Rural Affairs, says she’s additionally getting a number of reviews of the pest. Baute says that fields needs to be scouted twice every week a minimum of, however fields at larger danger together with people who had been seeded final 12 months, pure alfalfa stands, and areas of the sphere with south going through slopes, needs to be scouted first and probably extra usually.

For later harvested fields, similar to what Drew Thompson talked about in Niagara, fields go “silver” or “white” as a result of weevil skeletonize the leaves, the best high quality a part of alfalfa. In early harvested fields, they eat all of the regrowth and might severely injury stands (see above).

The financial threshold for management is 40 per cent leaf tip feeding and two energetic weevils per stem in mature alfalfa that won’t be harvested for seven to 10 days. Nevertheless it actually comes all the way down to the peak of the crop, Baute says, which after a chopping may be actually susceptible if the pest inhabitants will get forward of regrowth.

Scouting is finest completed within the early morning or nearer to night because the larvae could also be much less energetic in the course of the warmth of the day, Baute says. Scouting in early morning or nearer to night is at all times good as larvae could also be much less energetic in the course of the day, if temperatures are excessive. It’s the bigger larvae which might be used for figuring out thresholds. The smaller first two instars gained’t do as a lot feeding injury, she says.

Sweep nets can provide you a fast indication as as to whether or not the larvae or grownup weevil are current, however thresholds are primarily based on pulling crops and knocking them in a bucket to ascertain larvae counts.

Baute provides that ladybeetle adults like to eat younger larvae, as do different predators like spiders and damsel bugs. There are parasitoids (on this case, tiny wasps) which might be actually vital too, which is why the most effective management is to cut the stand to preserve high quality and knock again the pest.

The edge in harvested alfalfa simply starting to regrow is 2 larvae per crown or 4 larvae per sq. foot.

For extra data, see Ontario’s Agronomy Information, Publication 811, pages 339 to 340.


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