In the preemergence test, flumioxazin at 0.1 to 0.3 lb AI/A severely reduced the onion crop stand. Flumioxazin applied caused significant onion injury of 23 to 37% at 2 WAT for rates of 0.04 to 0.1 lb AI/A. Fluroxypyr and carfentrazone applied postemergence did not show any onion injury at 5 WAT. Fluroxypyr and carfentrazone did not offer acceptable control of annual yellow sweetclover at any rate. Carfentrazone at 0.063 lb AI/A demonstrated activity on lambsquarters and control nearly approached acceptable levels at 83% after 5 WAT. Fluroxypyr did not provide acceptable control of lambsquarters.

Efficacy of the grass herbicides showed that Select (clethodim) and BAS-620 (BASF Corporation) at rates as low as 0.1 lb AI/A were nearly comparable in controlling 2 leaf stage of growth watergrass or when applied a week later on 3-4 inch tall watergrass. Fusilade DX (fluazifop-p-butyl) was intermediate in controlling grasses and 0.188 lb AI/A was necessary to give equivalent control of larger grasses as compared to the 0.1 lb AI/A rate that gave acceptable control of smaller grasses. Poast (sethoxydim) at 0.188 lb AI/A gave acceptable control of small grasses but lower rates or later timed applications were not as efficacious.

In the preemergence test, azafenidin, flufenacet, thiazopyr, isoxaben, dithiopyr, and thifensulfuron exhibited safety on cantaloupes and watermelon at rates higher than rates required for effective weed control. In the postemergence test, the margin of selectivity for melon safety and weed control was narrow for MKH-6561, flufenacet, and thifensulfuron. MKH-6561 and CGA-362622 applied preemergence did not offer any acceptable crop safety relative to the weed control that was observed. Azafenidin, thiazopyr, isoxaben, and pyrithiobac did not demonstrate adequate melon safety compared to providing good weed control.

Halosulfuron applied POST with an adjuvant and ammonium sulfate was effective against lambsquarters and nutsedge. Rimsulfuron, flumetsulam, and thifensulfuron were effective against the pigweeds and purslane with minimal activity against lambsquarters. Halosulfuron and rimsulfuron were safe on melons and flumetsulam and thifensulfuron were marginally safe on cantaloupes. The combinations of these products may offer broader spectrum weed control.

Studies were conducted to determine the optimum time to apply glyphosate to glyphosate-tolerant Lactuca sativa cv. Raider (head lettuce). The study was initiated near Yuma, Arizona in September 2000. Single applications of glyphosate at 1.0 lb AI/A were made to head lettuce at development stages of 2, 4, 6 and 8 leaves. Glyphosate treatments did not injure lettuce. A single application at the 2 or 4 leaf stage was optimal for near complete control of Portulaca oleracea (common purslane), Chenopodium murale (nettleleaf goosefoot), Malva parviflora (cheeseweed), and Leptochloa spp. (sprangletop). Later applications at the 6 or 8 leaf stages allowed weeds, especially, common purslane to compete with the crop. Treatments applied at the 2 or 4 leaf stages required the least amount of time to hand weed and resulted in highest fresh weight yields.

Significant onion height reduction was observed when Prowl (pendimethalin) and Prefar (bensulide) herbicide combinations were applied preemergence (PREE). The onions resumed growth but the height was still slightly reduced later in the growing season compared to the handweeded check and the standard herbicide treatment, Dacthal (DCPA). The onion crop stand emerged initially but later in the season, a significant crop stand reduction was observed for the higher rate of Prowl at 0.5 lb AI/A plus Prefar. A lower rate of Prowl at 0.25 lb AI/A plus Prefar also caused a reduction of the onion stand compared to the handweeded check or Dacthal.

All herbicide treatments, Prefar, Frontier, Dual Magnum, Valor, and Prefar combined with Dual Magnum or Frontier caused less than 10% injury on cantaloupes. Frontier at 0.75 lb AI/A, Dual Magnum at 1.0 lb AI/A, Valor at 0.03 and 0.05 lb AI/A controlled weeds similar to Prefar. Prefar at 4.0 lb AI/A combined with Frontier controlled tumble pigweed (94%), narrowleaf lambsquarters (95%), Wright’s groundcherry (97%), and horse purslane (94%). None of the preemergence herbicide treatments controlled purple nutsedge.

Carfentrazone at 0.0125 and 0.025 lb AI/A was safe on all three lettuce cultivars. No stand reduction was observed. Sulfentrazone confirmed the initial screening test rate range of 0.05 to 0.1 lb AI/A for demonstrating marginal lettuce safety. Flumetsulam and thifensulfuron showed greater selectivity only in head lettuce while severely injuring romaine and red leaf lettuce. Rimsulfuron caused considerable stand reduction of all three lettuce cultivars. Sulfentrazone, fluroxypyr, and thifensulfuron exhibited good tolerance on broccoli as no stunting or stand reduction was observed at maturity.

Kerb (Pronamide) is often ineffective when it is leached below germinating weed seeds with sprinkler irrigation. Efficacy can be improved by making delayed aerial applications after the sprinklers have been started and before weeds have become established. Tests were conducted to determine the optimal time of application. Optimal times varied with the season and ranged from two to three days after the sprinklers had started during the early season (Sept.) to five to six days during the late season (January).

The 4lb/gal (4F) formulation of oxyfluorfen was significantly safer than the 2 lb/gal (2XL) formulation on broccoli when applied at the 2 or 3-leaf stages of growth. At 6 days after treatment of the first application at the cotyledon stage of the broccoli, significant injury to the broccoli ranged from 30 to 66% for all oxyfluorfen treatments. Crop stand reduction did not occur with either formulation. The 4F formulation at 0.25 lb AI/A gave nearly the same weed control as the 2XL formulation at 0.063 lb AI/A. The 4F formulation applied at the broccoli cotyledon stage of growth provided longer effective weed control for more than 3 weeks after applications. Later applications gave effective weed control for a period of time between 1 to 2 weeks.