Alfalfa Pest Updates Heath Sanders Area Agronomy Specialist Oklahoma State University March 21, 2018

Weed Infestations Limits yield potential Competition for resources Water Nutrients Sunlight Quality Tonnage Issues

Proper Weed I.D. is Critical Know and prioritize your weeds Broadleaf or grass What products can I use to control them? Correct timing Are they effective? Know the cost

Common Weeds Cutleaf Evening Primrose Henbit Prostrate spurge Chickweed Pigweeds Winter grasses Yellow woodsorrel Mustards Bermudagrass

Why Weeds? Little weed competition 30 alfalfa stems/sq.ft. Stands begin to thin Little weed competition 30 alfalfa stems/sq.ft. Reduced forage yield 20 alfalfa stems/sq.ft. Weeds may take over 10 alfalfa stems/sq.ft.

Weed Control in Alfalfa Established or Seedling Weed competition Type and severity Quality Tonnage Protein Market or Objective Can you allow for a few weeds?

Alfalfa Yield Reduction Weed competition in new stands of alfalfa often exceed 1,000lbs/ac Severe infestations can cause stand failure Thinning stands result in loss of ½ to 1lb/ac of alfalfa for every lb of weeds produced 30 stems of alfalfa /sq. ft. over entire field is defined as a full stand

Winter Annual Weed Competition Density Yield Loss (#/ft2) (% 1st Cutting) Henbit 10-20 None >20 Slight Sheperdspurse 1-4 5-10 >4 10-50 Tansy mustard 1-2 10-30 3-6 30-90 >6 50-100 Winter grasses 5-20 10-60 20-100

Herbicides for Seedling Stands Appl. Herbicide Method Balan PPI 8 5 9 Buctril 2 EC POST 6 Butyrac 200 Eptam 7-E 7 Cyclone Max Dorm. Kerb 50W Poast Pursuit 2 AS Raptor Select 2EC Annual Grasses Henbit Mustards Chickweed

Herbicides for Established Stands Appl. Herbicide Method Butyrac 200 POST 6 8 Cyclone Max Dorm/BC 9 Poast Pursuit 7 Raptor Roundup Select 2EC Sencor Dorm. Sinbar Velpar Annual Grasses Henbit Chickweed Lambquat. Pigweeds

Roundup Ready Alfalfa Good Potential for Weed Control Expensive System No residual control Expensive System Seed Cost Weed Resistance Concerns Apply a herbicide with residual during dormancy Then make in season application of Round-up

Roundup Ultra Max 40 fl oz/A 4 WAP Roundup Ready Alfalfa Roundup Ultra Max 40 fl oz/A 4 WAP Untreated

Roundup Ultra Max 40 fl oz/A 4 WAP Roundup Ready Alfalfa Pursuit 1.44 fl oz/A 7 WAP Roundup Ultra Max 40 fl oz/A 4 WAP

Cowpea Aphids Relatively easy to scout Color Female Smoky-gray nymphs Black- Adults Female Reproduce Asexually Various pressure levels 100/stem in some fields Fall Seeded 1-2/Plant can thin a stand under drought conditions

Alfalfa Weevil Weevil Populations remain low 3-5/30 stems with all being first instar Coincides with low egg counts observed earlier in the year

Treatment Considerations Based on number of aphids per stem Fall Seeded up to 5 per stem, Influence by environment Established Alfalfa, that has 10” of growth up to 50 per stem Insecticide treatment Lorsban Continues to be preferred choice 1 pt/ac show excellent activity Pyrethroid tank mix for weevils may be an option for some growers. Will we have to make a second application for weevils?? Not if numbers remain light

Thanks!