Wireworm Fields Wanted

With early season insect concerns becoming more common, we are looking for fields that have a history of wireworm problems to put out some insecticide screening trials. Preferably, these fields have a population confirmed this spring by the use of wireworm traps. Please contact Keith at 402-584-2261 or email him at kjarvi1@unl.edu if you are interested in helping us out. Thanks!

Watch for Alfalfa Weevil and Clover Leaf Weevil Activity:

Based on growing degree days, alfalfa weevils should be hatching from eggs and small pinholes may be visible in the new alfalfa growth near the tips of the plants. While alfalfa weevil damage has been spotty in much of Nebraska over the past few years, the potential for damage always exists. While things will be getting very busy in the next few weeks as row crops are to be planted, those of you who are growing high quality alfalfa hay should take the time to monitor fields for weevils over the next month.

Clover leaf weevils (CLW) are occasionally a problem but are very vulnerable to fungus disease and so haven't been pests since the late 80's early 90's when spring rains were rare. The dry conditions over the past several years may have aided them in building their populations, although rain over the last week could have knocked populations down. Clover leaf weevil larvae will be 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. Table 1 will compare the alfalfa weevil and the clover leaf weevil.

Both and alfalfa weevil and clover leaf weevils feed on first cutting alfalfa as larvae, and regrowth of the first cutting as adults. While research conducted in northeast Nebraska has shown that clover leaf weevil larva feeding does not cause yield reduction to first cutting alfalfa, alfalfa weevil feeding can cause severe losses to yield and quality of the first cutting.

Table 1. Comparison of Alfalfa Weevil to Clover Leaf Weevil.
Alfalfa Weevil	Clover Leaf Weevil
Overwinter primarily as adults	Over winter primarily as larvae
Adults brown with dark brown stripehalfway down back, 3/16 inch long	Adults dark brown, pitted light brown underneath, over 1/4 inch long
Larvae prefer to feed on tips	Larvae feed anywhere on plant
Larvae remain on plant most of the time	Many larvae in soil or debris during daytime hours
Larvae have black heads	Larvae have brown heads
Adults leave fields in June	Adults may remain in fields

It is essential that fields be monitored for alfalfa weevil feeding now. Damage consists of small holes and interveinal feeding on the newest leaflets near the stem tips. The larvae are a small (1/16 to 3/8 inch in length), pale yellowish green, becoming a darker green when larger. These legless worms have black heads and a white stripe the length of the back. The alfalfa weevil larvae spend nearly all their time on the plant. They curl into a C-shape when disturbed.

Once the alfalfa is about 4-6 inches or so in height, take a bucket, carefully cut some stems at ground level (30 to 50 per field, from various spots in the field) and shake the stems against the side of the bucket. Average the number of weevil larvae per stem. Use the following charts to aid you in making a decision on whether to control alfalfa weevils. Each chart has been developed for a different alfalfa value. To treat or re-sample depends on the average number of weevils per stem, the stem length, and the value of the alfalfa. When alfalfa reaches a certain height, it may be more profitable to cut the alfalfa early rather than to treat. Insecticides registered to control alfalfa weevil larvae include Ambush, Baythroid, Cythion, Furadan, Guthion, Imidan, Lannate, Lorsban, Mustang Max, Penncap M, Pounce, Sevin, and Warrior. Check the labels or see the Entomology Website at http://entomology.unl.edu/instabls/instabls.htm to find the use rates.

alfalfa weevil adult	alfalfa weevil feeding damage	alfalfa weevil larvae

Consider Spring Alfalfa Irrigation

Despite rain over the past week in some areas of northeast Nebraska, if dry conditions continue this spring, producers may need to irrigate alfalfa before May's first cutting. Drought continues in parts of Nebraska while elsewhere there is potential for another dry year. By irrigating alfalfa early, producers can more efficiently protect their stands through the summer.

Spring is the only time reserve water sources can be built up for summer use, and it usually hastens early alfalfa growth. With the low precipitation and soil moisture levels in many areas across the state, from now up until the first cutting is a good time to start irrigating alfalfa.

Western Nebraska is most likely to need irrigation, but even the eastern half of the state could hold more subsoil moisture. Irrigation is most effective when water reaches deep to the root base, where it can aid in root development. Alfalfa roots may reach depths of more than eight feet. Deep irrigation only works when there's plenty of moisture to meet crop needs so the extra irrigation can be used to saturate the soil all the way down to those depths.

Deep roots and moisture ease summer irrigating by providing extra moisture when plants use as much as half an inch of water per day. However, typical shallow summer irrigation encourages shallow rooting.

Irrigating now, when plants use less water and temperatures don't cause as much evaporation, is most efficient in the long run. Early, deep irrigation is like a water savings account that roots can tap if moisture is tight this summer. Bruce Anderson, Forage Specialist