Weed Control and Cantaloupe Tolerance to Halosulfuron W. C. Johnson, III Research Agronomist – Weed Science USDA-ARS Coastal Plain Experiment Station Tifton, GA

Halosulfuron Basics  Originally, a corn herbicide intended to be a replacement for atrazine  Reasonable broadleaf weed control spectrum  Good to excellent control of cocklebur, many pigweeds, ragweed, wild radish, and smallflower morningglory  Good to excellent control of yellow and purple nutsedge  No effect on grasses  Can be applied PRE or EPOST  Excellent results controlling nutsedge with either application

Halosulfuron Basics (cont.)  Little potential for carryover  4 to 12 day half-life in sandy loam soil  In contrast, Cadre has 120 day half-life  Symptomology  PRE applications Does not inhibit seed germination Does not inhibit seed germination Seedling growing point develops chlorosis and necrosis soon after seedling emergence Seedling growing point develops chlorosis and necrosis soon after seedling emergence  POST applications Chlorosis: 3-7 days after application Chlorosis: 3-7 days after application Necrosis of growing point: 7-14 days after application Necrosis of growing point: 7-14 days after application Complete death of plant: days after application Complete death of plant: days after application Weed size often determines how fast symptoms develop Weed size often determines how fast symptoms develop

Research on Halosulfuron Since 1995  Direct seeded cucumber and watermelon  Transplanted cantaloupe and watermelon on polyethylene covered beds  Times and methods of halosulfuron application on polyethylene covered beds  Residual benefits of halosulfuron applied to watermelon and sweet corn to future double- cropped crucifers

Weed Control Using Halosulfuron (2/3 oz./A) on Transplanted Cantaloupe Fl. pusley Smallflower morningglory Yellow nutsedge (1999) Yellow nutsedge (2001) (%) Metham fumigation Ethalfluralin Ethalfluralin + halosulfuron Nonfumigated Ethalfluralin

Visual Injury and Crop Yield Using Halosulfuron (2/3 oz./A) on Transplanted Cantaloupe Visual injury 1999 Visual injury 2001 Yield 1999 (no./A) Yield 2001 (no./A) Fruit size 1999 (kg/fruit) Fruit size 2001 (kg/fruit) (%) Metham fumigation Ethalfluralin Ethalfluralin + halosulfuron Nonfumigated Ethalfluralin

Weed Control with Halosulfuron (2/3 oz./A) in Transplanted Cantaloupe – Effects of Herbicide Placement Yellow nutsedge control Yellow nutsedge control – (%) Halosulfuron PPI under plastic 8882 Halosulfuron POST transplanting – OTT 9089 Halosulfuron POST transplanting - directed 9086

Crop Injury and Yield Response to Halosulfuron (2/3 oz./A) in Transplanted Cantaloupe – Effects of Herbicide Placement Visual injury Yield2000(no./A)Yield2001(no./A) (%) Halosulfuron PPI under plastic Halosulfuron POST transplanting – OTT Halosulfuron POST transplanting -directed Nontreated

Carroll Johnson’s Opinion on Halosulfuron  Best weed control spectrum of anything cucurbit growers would ever likely have registered  Significantly helps in the overall management of yellow and purple nutsedge  Controls several, but not all, broadleaf weed species  Application versatility (PRE or POST)

Carroll Johnson’s Opinion on Halosulfuron (cont.)  Acceptable crop tolerance among the cucurbit group  Most tolerant to least tolerant: Cucumber>cantaloupe=watermelon>squash  Safe application timings vary widely among cucurbit crops  My preference, based on considerable experience and research data is PRE to weeds but POST- Directed soon after transplanting This is a simple application technique that does not require significant reconfiguration of sprayers This is a simple application technique that does not require significant reconfiguration of sprayers

POST Transplanting – Directed Application for Herbicides

Carroll Johnson’s Opinion on Halosulfuron (cont.)  Cropping systems that routinely use herbicides such a halosulfuron will dramatically reduce populations of nutsedge since halosulfuron can control tubers. This may actually be the greatest benefit of halosulfuron in cropping systems that include vegetable crops.  Halosulfuron should not present a major carryover to other crops, either in single- or double-cropping systems.

Unanswered Questions  Refine the application timing by crop  Cultivar screening  Carryover to double- or rotation-crops  Sometimes seen, sometimes not seen – Why??? Interactions among pH, soil type, tillage, and water events Interactions among pH, soil type, tillage, and water events We will soon have the qualified personnel in place to answer these questions We will soon have the qualified personnel in place to answer these questions

Dan Evarts – the technician who makes my off- the-wall ideas work.