Alfalfa: Alfalfa weevil levels have been quite high in many fields. Alfalfa weevil larvae do not have legs, so can not move too far. Because of this early cutting is often an effective management strategy in hay crops. In seed crops management can be difficult. Insecticides are registered but often are not highly effective on alfalfa weevil.

 

Cereal Crops: Barley thrips are quite noticeable in some barley fields in Eastern Manitoba. To look for these, unroll the leaf sheaths away from the stem to look for the thrips. Most thrips will be under the top 2 leaf sheaths. Sampling for barley thrips is advised from when the flag leaf is first visible until the head is completely emerged from the boot.

Low levels of English gain aphid and oat-birdcherry aphid are being found in some fields. So far no fields have been reported near the threshold of 12 to 15 aphids per stem on average. Natural enemies can be found in some of these fields, including aphid mummies, which are the remains of aphids that have been parasitized by parasitic wasps. Heavy rains can also help reduce aphid levels.

Cereal Leaf Beetles Needed: Low levels of cereal leaf beetle have also been found in some fields. A parasitic wasp called Tetrastichus julis, which is specific to cereal leaf beetle, has been released in Manitoba in the past few years. It seems to be establishing well, and hopefully will keep populations at sub-economic levels. We are hoping to once again collect cereal leaf beetle larvae and determine the percent of larvae that are parasitized from fields in various regions. So if you are noticing any cereal leaf beetle larvae on wheat, oats, barley, or any other cereal crop, please collect a sample or let me know so we can collect some and determine the level of parasitism in the population. Areas that may have low levels of parasitism would be considered for possible future releases of the parasitoid. Ideally a sample of at least 30 larvae is good for estimating percent parasitism. They can be collected off the plant or in a sweep net. Place some food for them in the container as well. The larvae often have a fecal coating over them, and may look like a drop of oil on the plant. 

  
  Figure 1. Larva of cereal leaf beetle.         Figure 2. Feeding from cereal leaf beetle.

 

Pulse Crops: Pea aphid is showing up in some pea crops. Whether it would be economical to use an insecticide to manage aphids in peas depends on the levels that is present. The economic threshold is: If, at the beginning of flowering, there are 9 to 12 aphids per sweep or 2-3 aphids per 8-inch (20 cm) plant tip, an insecticide application when 50 percent of plants have produced some young pods will be cost-effective. Whether aphid levels increase, and to what extent, depend on the levels of natural enemies that are present, and possibly weather conditions (heavy rains can sometimes decrease a population).

To date there have been no reports of soybean aphids in Manitoba this year.

 

 

 

Question: A couple of enquiries have come in recently regarding these slug-like animals on plants, that seem to be probing around with their narrower tapered end. What are these?

Answer: These are larvae of hover flies. They are predators. One of their favorite foods is aphids. You will note that they have no legs. The tapered end is their head of the insect. If you see them near an aphid colony, you may get to witness them impaling an aphid, holding it up and sucking the fluids out of it - super fun to watch while out crop scouting.