Diquat was tested to determine its suitability for use as a preharvest desiccant of selected vegetable seed crops during 1997 and 1998. In separate studies, diquat was applied at 0,0.56, or 1.12 kg·ha-1 ai. to spinach (Spinacia oleracea L.), table beet (Beta vulgaris L.), and coriander (Coriandrum sativum L.) plants at usual swathing time. Except for beet seed in 1998, there was no clear trend toward reduced seed weight with increasing diquat rate. Spinach seed germination in 1998 and coriander seed germination in 1997 were reduced by diquat at 1.12 kg·ha-1 compared to seed from nontreated plants or plants treated with 0.56 kg·ha-1. In all crops, diquat at 0.56 kg·ha-1 was adequate for crop desiccation purposes. However, seed producers should consider the potential benefits from chemical desiccation that may potentially lower germination of the harvested seed. Chemical name used: 6,7-dihydrodipyrido[1,2-α:2′,1′-c]pyrazinediium ion (diquat).
Tulip, narcissus, and bulbous iris are grown on about 1600 acres annually in western Washington. These bulb crops are poor competitors with winter annual weeds that continually germinate from September through July in the mild maritime climate of this region. Because they do not adequately control emerged weeds but can injure bulb crop foliage, herbicides are applied in the fall. Unfortunately, fall-applied herbicides lack the soil persistence necessary for season-long weed control. If nonselective herbicides could safely be applied after emergence of bulb foliage, emerged weeds would be killed and the application of residual herbicides delayed until spring, thus lengthening the period of weed control through bulb harvest. Glyphosate was tested for selectivity at three postemergence timings (early, middle, and late) on four cultivars each of tulip and iris and three narcissus cultivars. Middle and late glyphosate treatments caused severe injury to tulip foliage and flowers and reduced bulb count and weight, but early glyphosate did not significantly injure most varieties. Narcissus and iris were more tolerant to glyphosate than tulip, but these species also were most tolerant when glyphosate was applied early. In a separate study on iris, carfentrazone, paraquat, and glufosinate were applied postemergence at the same three timings. Glufosinate initially caused moderate injury to foliage (about 20%), but plants quickly recovered. Injury from carfentrazone and paraquat was much more severe (more than 50%), although plant recovery from carfentrazone damage was greater than from paraquat. Bulb yield was not adversely affected by either glufosinate or carfentrazone if applied early. Paraquat at all timings significantly reduced total bulb count and weight.
A large percentage of North American processing red raspberry (Rubus idaeus L.) is produced in maritime areas of western regions in Washington, British Columbia, and Oregon. Most of these raspberry plantings are caneburned; they are treated with herbicides in early spring to remove the first-emerging primocanes in an attempt to reduce their competition with floricanes during flowering and fruiting and thereby increase fruit yield. Trials were conducted in northwestern Washington to determine the effect of carfentrazone and oxyfluorfen applied for primocane management in three currently grown raspberry cultivars. Although caneburning did provide early season weed control in treated plots, weed control fell below 70% in the commercial ‘Meeker’ field more quickly each year: at 138 days after treatment (DAT) in 2010, 71 DAT in 2011, and 47 DAT in 2012, compared with greater than 80% control at the end of each season when the soil residual herbicide terbacil was applied. Oxyfluorfen provided longer suppression of primocane growth than did carfentrazone, particularly in ‘Cascade Bounty’ but also to a lesser extent in ‘Meeker’. Caneburning did not improve raspberry yield in five of the six tested years for ‘Meeker’, or in any of the five tested years for ‘Cascade Bounty’ or the single year for ‘Coho’, although the trend was for greater yield with caneburning across all cultivars. Oxyfluorfen improved 3-year ‘Meeker’ average yield 43% from nontreated raspberry in the commercial field trial, compared with a 29% increase with carfentrazone.
Propane flaming and organic amendments were evaluated for usefulness in matted-row strawberry (Fragaria ×ananassa Duch.). Flaming was used once before transplanting ‘Hood’ strawberry (PRETR), twice before transplanting (PRETR + PRETR), or once before and once after transplanting (PRETR + POSTR) and compared with rototilling before transplanting in 2000–02. Organic amendments tested across flame treatments included corn gluten meal (CGM) at two rates, wheat gluten (WG), and mustard seed meal (MSM) with high or low glucosinolate content, and herbicides included oxyfluorfen, pendimethalin, and a combination of oxyfluorfen + pendimethalin. Amendments/herbicides were applied immediately POSTR in Year 1 and again to established plants in late winter of Year 2. All plots were weeded by hand after weed evaluations were completed and weeding hours recorded. The trial was conducted twice: Iteration 1 and Iteration 2. Effect of flaming on grass and broadleaf weed ratings was brief during Year 1 of both iterations, with only slight differences observed in June and no differences by September. Total weeding time was reduced 12% by flaming PRETR once compared with rototilling in Iteration 1 and was reduced 10% by all flame treatments in Iteration 2. Rototilling reduced total berry yield and average individual fruit weight compared with flaming treatments in Iteration 1; there was no significant effect of flame on strawberry yield or individual fruit weight in Iteration 2. Organic amendments did not reduce weeding time in Iteration 1 compared with the nontreated control, although weeding time was increased 18% by CGM at 487 kg·ha−1 compared with synthetic herbicide treatments. In Iteration 2, total weeding time was reduced 14% for the two pendimethalin treatments and for high-glucosinolate MSM compared with nontreated control plots. First-year strawberry leaf area was reduced by oxyfluorfen + pendimethalin compared with nontreated strawberries (802 and 1086 cm2/plant, respectively) and was generally increased with organic amendments. Strawberry yield in Iteration 1 was increased ≈14% by CGM at 974 kg·ha−1 and WG and low-glucosinolate MSM compared with nontreated strawberry. Oxyfluorfen and oxyfluorfen + pendimethalin reduced strawberry yield by ≈20% and average individual fruit weight by ≈9% (14.8 and 14.5 g/fruit) compared with nontreated strawberry (16.1 g/fruit); high-glucosinolate MSM also reduced average individual fruit weight to 14.8 g/fruit. There were no significant effects of amendments/herbicides on strawberry yield parameters in Iteration 2.