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.
With the end of lettuce season, it does feel like a relief from the recent INSV (Imaptiens necrotic spot virus) breakout we had. However, we have to keep in mind that INSV has a very wide host range. It is a common virus in ornamentals. Below is just a small list of ornamental plants that could be a host of INSV. If you have these plants and see any concerning symptoms, please bring them to the plant clinic to test for INSV.
INSV is the first virus to be recorded from a fern (the glasshouse ornamental Asplenium nidus-avis).
|Dendranthema x grandiflorum||Eustoma grandiflorum|
|Gladiolus||Imaptiens (New Guinea, Balasam)|
|Senecio cruentus||Sinningia speciose|
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://18.104.22.168:460
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.
Beet armyworm: Moth activity has declined in most trap location and remains below average for this point in the season.
Cabbage looper: Cabbage looper activity remains unusually low for early November. Trap catches picked up a bit in Wellton and Gila Valley.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton near fall melons being harvested.
Thrips: Thrips activity picking up significantly in several trap locations; activity increased significantly in Bard and Dome and Gila Valleys.
Aphids: Aphid numbers peaked last week in many locations, particularly in the Gilas and Yuma Valleys.
Leafminers: Adult activity increased significantly last week, particularly in the Wellton area near melons.