May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
When known weedy fields are ready to plant and labor is expected to be short, it is tempting to use all the preplant herbicides that are available. In lettuce, there are three preplant herbicides available and it is not uncommon to use 2 and occasionally all 3 on the same crop. All three of these herbicides use the same mode of action to kill weeds. There are slight differences between them but they all either stop or disrupt cell division in the roots and or stems of the weeds. They are normally safe to lettuce unless the crop is stressed or the rate, timing or placement are poor. The rationale for using multiple preplant herbicides in lettuce is often to broaden the weed control spectrum or guard against misses caused by misapplication or environmental conditions. There are some hazards, however, that sometimes outweigh the benefits. Potential crop injury is increased. All 3 use the same mode of action and the chance of injuring developing crop roots is compounded. Sometimes herbicides are added that contribute nothing but potential injury to the mix. If you look at the following chart you can see that many weeds are controlled by Kerb, for instance, that are not controlled by Balan or Prefar. Why add them? All three control grasses, goosefoot and purslane. If environmental conditions and applications are optimal it is often possible to use only one. Herbicides are much less expensive than labor, but it is possible to overdo it and cause more problems and expense.
We have learned a lot about viruses and one of the striking features of most plant viruses is that they always need a host. And the relationship between a virus and its host plant is very specific. So where do the viruses go when we do not have lettuce or melon in the field? And how do they come back at the right time to infect the crops? (clue insect vector). The answer is weeds. A lot of the most economically important viruses are economically important viruses not just because of the losses they cause, but also because of the losses they cause in variety of plants. Viruses have small genome size that allows them to evolve faster. Viruses over time have evolved to adapt and increase their host range.
Below are some common viruses in agriculture and the number of plants they infect/overwinter. Keep in mind that there are many plants that can act as a reservoir for virus but have not been reported yet, so this is not an exclusive list.
Alfalfa mosaic virus (AMV): Alfalfa, lettuce, endive, sunflower, datura, amaranth, different species of pigweed, milkweed, annual fleabane, oxeye daisy, hairy galinsoga, smallflower galinsoga, different species of mustards, common lambsquarters, hedge bindweed, field bindweed, cucurbits, different species of clover and vetch, beans, broad beans, lima beans, lupine, pea soybean, ground Ivy, healall, okra, purslane, pimpernel, black nightshade, pepper, tomato, petunia, eggplant, potato, garden pansy etc.
Cucumber mosaic virus (CMV): pigweed, horseweed, oxeye daisy, coffee weed, Canada thistle, bull thistle, hairy galinsoga, Jerusalem artichoke, prickly lettuce, wild chamomile, hawkweed, groundsel, Canada goldenrod, sowthistle, endive, sunflower, lettuce, mustard, radish, chickweed, lambs quarters, morning glory, cucurbits, common teasel, alfalfa, beans, lima beans, mung beans, geranium, ground Ivy, okra, purslane, jimsonweed, ground cherry, horsenettle, black nightshade, pepper, tomato, petunia, eggplant, potato, burning nettle, garden pansy.
Lettuce mosaic virus (LMV): lettuce, bristly oxtongue, spinach.
Bidens mottle potyvirus: lettuce, endive, horseweed, hairy beggarticks, virginia pepperweed, Mexican pricklepoppy.
Celery mosaic virus (CeMV): Celery, giant hogweed
Papaya ringspot virus (PRSV): Bur cucumber, creeping cucumber, balsom pear, cucumber, cantaloupe, watermelon, summer squash, pumpkin, gourd, winter squash, butternut squash,
Tomato spotted wilt virus (TSWV): Tomato, potato, pigweed, hairy beggarticks, oxeye daisy, coffeeweed, prickly lettuce, annual sowthistle, ebdive, sunflower, lettuce, shepherd’s pruse, chickweed, hedge bindweed, cantaloupe, muskmelon, bean, broad bean, mung bean, cutleaf evening primerose, broadleaf plaintain, purslane, jimsonweed, bittersweet nightshade, black night shade, pepper, tomato, petunia, eggplant, potato.
Tobacco mosaic virus(TMV): White campion, jimsonweed, pepper, tomato, tobacco.
Turnip mosaic virus(TurMV): pigweed, wild carrot, bachelo’s button, Canada thistle, hairy galinsoga, smallflower galinsoga, common catsear, pineapple weed, dandelion, endive, sunflower, lettuce, mustard, brassicae crops, corn cockle, chickweed, common lambsquarter, spinach, cucumber, alsike clover, lupine, redstem filaree, ground Ivy, okra, velvetleaf, common pokeweed, purselane, jimsonweed, black nightshade, tomato, petunia..
Watermelon mosaic virus (WMV) : mustard, common lambquarters, spinach, cucumber, watermelon, cantaloupe, squash, buttercup, red clover, common vetch, alfalfa, beans, lupine, pea, henbit, common mallow, okra, common pokeweed, jimsonweed, nightshade,
Zucchini yellow mosaic virus (ZYMV) : cucumber, cantaloupe, watermelon, squash, zucchini, pumpkin, gourds.
Mark C. Siemens
Vol. 12, Issue 9, Published 5/5/2021
Automated thinning machines have been commercially available since 2012. These machines identify crop plants and intermittently deliver an herbicidal spray or dose of liquid fertilizer to thin the stand to the desired plant spacing. Some growers have converted older machines to spot apply pesticides to crop plants rather than thin lettuce. Spot spraying just the crop plant makes sense – it reduces applied chemical amount by about 1/3rd as compared to band spraying and by roughly 90% as compared to broadcast. I have heard reports of improved efficacy with this technique, perhaps due to better coverage, however this potential benefit has not been validated in formal trials.
A drawback with automated thinning machines is their high cost. Retail prices for machines are approximately $25,000 per seed line, or about $200,000 for a 4-row, 2-line machine. Another option might be to use automated systems designed for spot spraying weeds. These devices have been commercially available since the mid 90’s and function similarly to automated thinning machines in that they use optical sensors to detect plants and solenoid activated spray assemblies to intermittingly spray unwanted plants (Fig. 1). The cost of these devices is quite reasonable – about $3,000 per unit, or about $24,000 for a 4-row, 2-line machine.
Automated spot sprayers are typically used in agriculture to control weeds in fallow fields (Fig. 2), but could easily be adapted to apply pesticides or even fertilizer to vegetable crops. Spot applying foliar fertilizers to vegetable crops is an interesting concept and is being investigated in California with lettuce.
Another potential use of spot sprayers is to control herbicide resistant weeds. The device can be positioned between crop rows to spot spray a non-selective herbicide to target weeds. Placing the sprayer in a hooded enclosure prevents unwanted drift onto crop plants. We are conducting trials using this technique in cotton this season (Fig. 3). We are also looking for collaborators interested in trying the device as a pesticide and/or fertilizer spot applicator in vegetable crops for this upcoming season. If you are interested collaborating or would like to see a demo of the device, please feel free to reach out to me.
Growers and PCAs can monitor data from the Yuma Leaf Wetness Network through the AZMET website located at the following URL: http://22.214.171.124:460
The website updates information on leaf wetness and near-surface air temperature every 15 minutes. Wetness data are provided in graphical format (see figure below). Output from the leaf wetness sensors increase from the grey (dry) zone of the graph to the blue (wet) zone when wetness (dew or rain) is detected by the sensors.
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 21, October 14, 2020
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard. Numbers beginning to slowly trend upward
Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year. Still early, anticipate they will begin to show up in heavier numbers in mid-late October.
Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.