Authors
John J. McHugh, Jr. and Ronald F. L. Mau
Department of Entomology
Honolulu, Hawaii
Disease |
Control Measure(s) |
Comments |
| Alternaria purple blotch and Botrytis leaf blight | Crop rotation. Iprodione (Rovral 4F) at 1.5 to 2 pt. per acre in 50 gal. water. Dry bulb onions only. Chlorothalonil (Bravo, Terranil) at 1 to 3 pt. per acre (F flowable products) or 0.875 to 1.75 lb. per acre for dry formulations (DF, DG). Mancozeb (Dithane, Manzate, Penncozeb or Manex II) at 4.8 pt. per acre for flowables or 3 lb. per acre for dry products (WP, DF, DG). Dry bulb onions only. Copper sprays at labelled rates at first sign of disease symptoms. See Hawaii Pesticide Information Retrieval System for Information on onions |
2 - 3 year minimum rotation
to non-host crop can reduce soil innoculum. PHI for iprodione = 7 days. PHI for chlorothalonil = 7 days for dry bulb onions, 14 days for green onions. PHI for mancozeb = 7 days. |
| Bacterial soft rot (Erwinia caratovora subsp. caratovora) | Avoid overhead irrigation/excessive water during bulb formation. | Disease is soilborne and may be spread through irrigation water. |
| Downy mildew | Metalaxyl and mancozeb
(Ridomil Gold MZ) at 2.5 lb. per acre.Dry bulb
onions only. Metalaxyl and chlorothalonil (Ridomil Gold Bravo) at 2 lb. per acre. Chlorothalonil (Bravo, Terranil) at 1.5 to 3 pt. per acre (F flowable products) or 1.125 to 2.25 lb. per acre for dry formulations (DF, DG). Mancozeb (Dithane, Manzate, Penncozeb or Manex II) at 4.8 pt. per acre for flowables or 3 lb. per acre for dry products (WP, DF, DG). Dry bulb onions only. Fosetyl-al (Aliette 80WP) at 2 to 3 lb. per acre. Dry bulb onions only. Copper sprays at labelled rates at first sign of disease symptoms. See Hawaii Pesticide Information Retrieval System for Information on onions |
Disease favored by cool,
moist conditions. Begin spraying when conditions are
favorable. Ridomil Gold MZ PHI = 7 days. Ridomil Gold Bravo PHI = 7 days for bulb onions, 14 days for green onions. PHI for chlorothalonil = 7 days for dry bulb onions, 14 days for green onions. PHI for mancozeb = 7 days. Aliette PHI = 7 days. |
| Pink root (Phoma terrestris) | Resistant varieties. Pre-plant injection with Telone C-17 at 24 to 27.5 gal. per acre. |
Check with seed dealers. Check with manufacturer for recommended injection methods. |
| Root-knot nematode | Pre-plant injection with Telone C-17 at 24 to 27.5 gal. per acre. | Check with manufacturer for recommended injection methods. |
| Stemphylium leaf blight | Chlorothalonil (Bravo,
Terranil) at 1.5 to 3 pt. per acre (F flowable products)
or 1.125 to 2.25 lb. per acre for dry formulations (DF,
DG). Mancozeb (Dithane, Manzate, Penncozeb or Manex II) at 4.8 pt. per acre for flowables or 3 lb. per acre for dry products (WP, DF, DG). Dry bulb onions only. |
PHI for chlorothalonil = 7
days for dry bulb onions, 14 days for green onions. PHI for mancozeb = 7 days. |
Insects/Mites |
Control Measure(s) |
Comments |
| Caterpillars: Beet armyworm, leek moth |
Lambda-cyhalothrin (Karate
or Warrior 1E) at 1.92 to 3.84 fl. oz. per acre. Dry
bulb onions only. Methomyl (Lannate 90 or LV) at 0.5 to 1 lb. per acre for 90 or 1.5 to 3 pt. per acre for LV. See Hawaii Pesticide Information Retrieval System for Information on onions |
Do not apply more than 1.92
pt. of Warrior 1E per acre per season; PHI = 14 days. Lannate PHI = 7 days. |
| Onion thrips | Lambda-cyhalothrin (Karate
or Warrior 1E) at 1.92 to 3.84 fl. oz. per acre OR
cypermethrin (Ammo 2.5 EC or WSB) at 2 to 5 fl.
oz. per acre for EC or 1 to 2 bags per acre WSB). Dry
bulb onions only. Methomyl (Lannate 90 or LV) at 0.5 to 1 lb. per acre for 90 or 1.5 to 3 pt. per acre for LV. See Hawaii Pesticide Information Retrieval System for Information on onions |
Do not apply more than 1.92
pt. of Warrior 1E per acre per season; PHI = 14 days. Do not apply 0.5 lb. a. i. of Ammo per acre per season, PHI = 7 days. Lannate PHI = 7 days. |
| Seedcorn maggot | Diazinon (Diazinon AG500,
14G) at 2 to 4 qt. per acre for AG500 or 14 to 23 lb. per
acre for 14G. Chlorpyrifos (Lorsban 4E or 15G) at 1.1 fl. oz. per 1000 row ft. for 4E or 3.7 oz. per 1000 row ft. for 15G. Dry bulb onions only. See Hawaii Pesticide Information Retrieval System for Information on onions |
Diazinon most effective
applied as a preplant and incorporated, PHI = 14 days. Chlorpyrifos applied pre-plant and incorporated. |
| Pea leafminer Vegetable leafminer Chrysanthemum leafminer
|
Conserve natural enemies. See Hawaii Pesticide Information Retrieval System for Information on onions |
Minimize use of organophosphate, carbamate and pyrethroid insecticides. Pyrethroid insecticides (Warrior and Ammo) and methomyl are highly toxic to leafminer natural enemies. |
Control Measure(s) |
Rates |
Comments |
| Glyphosate (Roundup Ultra WS) or Paraquat (Gramoxone Extra 2.5E) | Roundup Ultra WS at 0.5 - 10
pt. per acre (higher rates for difficult to kill weeds,
for example, purple nutsedge). Gramoxone Extra 2.5E at 1.5 to 3 pt. per acre. |
Stale seedbed treatments. Broad spectrum weed control. Preplant control of purple nutsedge is extremely critical to a successful onion crop. |
| Pendimethalin (Prowl 3.3EC
or Pentagon DG) See Hawaii Pesticide Information Retrieval System for Information on onions |
1.2 to 3.6 pt. per acre for Prowl, 0.85 to 2.5 lb. per acre for Pentagon. For use on bulb onions only. | Preplant
incorporated/Preemergent. Mostly grass control but some broadleaves. PHI = 45 days. |
| Oxyfluorfen (Goal 2XL) | 2 to 4 fl. oz. per acre. For use on bulb onions only. | Postemergent/Preemergent.
Apply after 2 true leaf stage. Up to 3 applications may
be needed. Can cause phytotoxicity, especially if applied
during extended cloudy, humid periods. PHI = 45 days. |
| Fluazifop-p-butyl (Fusilade DX) | 0.375 to 0.75 pt. per acre plus 1 pt. Herbimax surfactant per acre. | Postemergent/Postplanting. Grass control. Apply to actively growing grasses. PHI = 45 days. |