When scouting alfalfa, there are two species of weevils that may be observed. These two species are the alfalfa weevil and the clover leaf weevil. The alfalfa weevil is known to cause serious defoliation and has the greater potential to cause yield losses. However, clover leaf weevils can also become very damaging if present in large populations. Although they are similar in size and coloration, there are some distinguishing characteristics that can be used to identify these weevil species.
Over the last few weeks, we received reports of two spotted spider mite infestations in alfalfa. The twospotted spider mite is capable of feeding on a wide variety of plants including soybean, alfalfa, and corn. Twospotted spider mites are generally not an issue in alfalfa; however, dry conditions similar to those that have been experience in South Dakota for the last couple of weeks can allow for infestations to occur. Recent rains may help reduce the twospotted spider mite populations, but it will be very important to scout alfalfa fields to ensure that infestations do not cause yield reductions.
While scouting alfalfa last week we observed populations of pea aphids throughout much of the field. We also received reports of fields that have a golden hue and large populations of pea aphids present in south central South Dakota. The golden hue that is being observed is due to pea aphid feeding, and is an indicator that a large population may be present. The presence of pea aphids in alfalfa is common, but if they reach large populations there is the potential for yield reductions to occur.
As the first cutting of alfalfa is approaching there are several insect species to scout and monitor for. While scouting alfalfa last week I encountered what at first I thought were large populations of potato leafhoppers. However, upon closer inspection using a hand lens it was clear that they weren’t potato leafhoppers but instead aster leafhoppers.
This week we received a report of insecticides being applied to manage alfalfa weevils in South Dakota. In 2016, we believed that the reports that we received during the same time period in May were early. Now, it appears that populations may simply be present earlier in alfalfa than previously reported for the state.
Producers are trying to get their alfalfa planted. Some areas have been very wet which have made this process very difficult to accomplish. Here are some considerations to keep in mind when planting alfalfa this growing season.
Bacterial blight tends to show up when pea plants are damaged by rain, wind, hail or a late spring frost. Tissue damage to the plant will create a wound and the bacteria will colonize the wound. Symptoms of bacterial blight can appear on the stem, leaves and pods of the pea plants. All foliar tissue is susceptible. Initial symptoms are small shiny water soaked spots. As the disease progresses these areas can coalesce, and turn brown and necrotic.
There are several species of grasshoppers that can negatively affect rangeland conditions in South Dakota. Grasshoppers tend to be more serious than other rangeland insect pests, and they occur most frequently. Each summer, the United States Department of Agriculture’s (USDA) Animal Plant Health Inspection Service (APHIS) conducts surveys throughout the Western counties to monitor grasshopper population densities. These surveys focus on collecting adult grasshoppers, and the data can be used as a prediction of areas where grasshoppers may be an issue during the following year.
This year lack of snow coverage along with up’s and down’s in temperatures have caused several issues with alfalfa stands in several locations in South Dakota. Where the damage has occurred, it is concentrated in areas of fields where ice sheets formed, water ponded, poor drainage, and not enough snow cover to insulate alfalfa against extreme temperatures. Late harvested stands that are three or more years old are showing more damage than younger ones’ under moderate management.
A field scale replicated trial testing different fertilizer nitrogen rates on sorghum was conducted in Stanley County during the summer of 2016. In addition to the standard testing procedure, the laboratory also ran the Haney suite of tests. This is a set of procedures developed by Dr. Rick Haney. It is being promoted in some areas as being able to do a better job of predicting fertilizer requirements than traditional testing procedures when no-till and cover-crop techniques are being used.