STRAIGHT FROM THE HORSES MOUTH



Duane A. Lienemann,

 UNL Extension Educator,
 Webster County
It is the season for scouting …even though it is a couple of weeks early. It seems that everything has the jump on development this year, from wheat to weeds and from bugs to buds. I think it may be good to take a look at a couple of things this week along that line. As with everything else this year the wheat crop is approximately two weeks ahead of normal crop development due to unseasonably warm temperatures in the winter and of course this spring.
Wheat Concerns: Above normal temperatures are forecast for the coming weeks even though there is still a threat of an early spring frost. Now with the recent nice rainfall in this area, the combination of warm temperatures and moisture can lead to rapid development of foliar wheat diseases including powdery mildew and fungal leaf spots. These have already been observed in southeast Nebraska and in north central Kansas. There also have been reports of general yellowing of wheat fields. I have stopped to take a look at a couple of them in Webster County. This condition is common at the current growth stage and can be caused by several factors, including inadequate fertilization and viral diseases. If the yellowing is of a general nature with no obvious virus symptoms (stunting and leaf mosaics, mottling, or streaking), it is most likely due to inadequate fertilization. The wheat crop usually grows out of this condition and greens up as the growing season progresses. I think around here it is more environmental yellowing rather than disease. Some fields that I looked at had some burn from fertilizer application, but should come out of that without any trouble.
As always I recommend that if you have any wheat fields that you scout them routinely for early detection of diseases and perhaps for small dark Bird Cherry Oat Aphids (Barley Yellow Dwarf virus vector). That does not mean a windshield tour. You need to walk through the fields and look at into the wheat growth. This will facilitate timely management decisions. Except in fields where disease pressure is high early in the growing season, fungicide application to control foliar fungal diseases should be aimed at protecting the flag leaf. I usually don’t get too excited until I know that my flag leaf is emerging, but it is nice to know what is out there and if we need to suppress the diseases early or not. If you do need that you have to spray on a fungicide early, you should be aware that it may be necessary to apply a second spray at early flowering to suppress Fusarium head blight (scab) in scab-prone areas. We did have that in a lot of fields last year.
Alfalfa Weevil: I have found several fields with Alfalfa Weevil larvae working on the plants. I suggest that if you have alfalfa that you scout your fields now. Most alfalfa weevils overwinter as adults, become active as temperatures increase, and lay eggs. Some may lay eggs in the stem during fall and, if winter is not too severe (which fits this year’s scenario), will successfully overwinter. These eggs will hatch earlier than those laid in spring. This is most likely to occur in southern counties (again fitting the scenario perfectly). Since they have had an early start, they can seriously damage growing alfalfa. Damage consists of small holes and interveinal feeding on the newest leaflets near the stem tips. They can skeletonize a leaf or series of leaves on a plant. As feeding increases, the field begins to take on a grayish tint. The larvae are small (1/16 to 3/8 inch long) and pale yellowish green, becoming a darker green when larger, with black heads and a white stripe the length of the back. The alfalfa weevil larvae spend nearly all their time on the plant. They will curl into a C-shape when disturbed.


We really should have been monitoring fields as soon as alfalfa is 4 to 6 inches tall, and there is some about at that stage and some fields are beyond that, but still should be checked. If you see damage, carefully cut 30 to 50 stems per field to ground level and shake the stems against the inside of a 5 gallon bucket. I prefer using a white bucket. Count the number of weevil larvae in the bucket and determine the average number per stem. You might also consider using a sweep net as you walk through the field if you have one. Economic thresholds and insecticide recommendations can be determined by referring to the NebGuides located at: http://cropwatch.unl.edu/web/insect/alfalfapests   or call our office.
If control is recommended, either harvest alfalfa early or use insecticides. I actually prefer to harvest if you are within ten days of first cutting because you save on insecticide cost and loss of beneficial insects. But if you choose to spray there are several insecticides are registered to control alfalfa weevil larvae including Ambush, Pounce, Mustang, and Warrior. Highly effective insecticides for alfalfa weevil control include those that are pyrethroids (active ingredient ends in “thri”). You may want to note that pyrethroid insecticides also can have detrimental effects on any beneficial insects present.
Just to add to worries you may want to remember that Clover Leaf Weevils are occasionally a problem. To scout for clover leaf weevil, look in the debris around the crowns during day. Scratching in the soil around the crowns and counting the number of larvae found per crown will help give a better idea of clover leaf weevil infestation. Their brown heads will help distinguish them from the black-headed alfalfa weevil. Both and alfalfa weevil and clover leaf weevils feed on first cutting alfalfa as larvae, and regrowth after the first cutting as adults (and sometimes larvae). While research has shown that clover leaf weevil larva feeding doesn’t cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting. This is why it’s important to correctly identify the type of weevil feeding causing damage. Monitor your wheat and alfalfa fields. This may be the year that will pay for your effort!
The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the website at: www.webster.unl.edu/home