May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Clovers can be very difficult to control weeds here, but it is also a major crop and common ornamental. Clovers can survive under poor growing conditions and are not controlled with glyphosate and seem to get worse every year. There are more than 50 types and 300 species of clover and they can be easily misidentified. They are all in the legume (Fabracea) family and can use a bacterium (rhizobium) in the soil to convert nitrogen in the atmosphere to a form that they and other plants can use for fertilizer. There are only 4 or 5 clover species that are agricultural pests here. The ones we get the most questions on are white and yellow sweet clover. These are in the Melilotus family. White sweet clover (Melilotus albus) is tall for a clover and can get 3 to 5 foot in height. The leaves are thinner than most clovers and this difficult to control weed lives at least 2 years and sometimes longer. Glyphosate and most of the contact herbicides do not control it. The plant growth regulator herbicides work best. Yellow sweet clover (Melilotus officinalis) is less common here. The flowers are yellow, and it is not as tall and vegetative as white sweet clover. Yellow is more common at higher elevations. California burclover (Medicago polymorpha) and Black medic (Medicago lupina) are in the same genus as alfalfa and are more of a problem in landscapes, parks and golf courses than in agricultural fields here. They do not grow upright and spread below the crop or turf. The true clovers are in the Trifolium genus and include white and strawberry clover. These creep along the ground and root at the nodes of the stem. These are more of a urban landscape weed and not considered an agricultural problem. Creeping woodsorrel or Oxyalis looks like a clover but it is not related. It is a turf weed that spreads rapidly along the ground and can live for several years. Preemergent herbicides are effective against all these clovers before they become established. The postemergence herbicides that are most effective in controlling these clovers are the plant growth regulators. Contact herbicides and glyphosate are generally ineffective.
With harvesting time getting closer to many field crops now, we are seeing higher incidence of bacterial diseases. We had few reports of bacterial spot on lettuce, cilantro, arugula, and parsley. Most times bacterial symptoms are not expected or simply ignored because we think the desert is too dry and bacterial diseases require high humidity. But as the plants grow bigger the space and aeration in between plants decreases, thus creating a humid microclimate. It is even more common on produces/herbs like cilantro, arugula, parsley etc. where the crops are grown densely, and sprinkle irrigation is used.
Initial symptoms of bacterial leaf spot are water-soaked lesions on leaves. The lesions develop into spots that are varying shades of tan or brown (see picture ‘B’ on parsley whereas advanced spots on cilantro can be black (see picture ‘A’ on cilantro). The lesions are usually limited by leaf veins and thus have an angular, square, or rectangular appearance, a typical feature of bacterial infection. Lesions tend to be relatively small about 1/8 to 1/4 inch (3–6 mm) in diameter and are visible from both the top and bottom of leaves. Under favorable conditions, free moisture from rain or sprinkler irrigation, leaf spots may coalesce and cause considerable blighting of the entire foliage.
Pseudomonas syringae pv. apii (Psa) and P. syringae pv. coriandricola (Psc). cause bacterial leaf spot on most vegetable. Pseudomonas syringae pv. apii (Psa) can cause leaf blight in celery and fennel as well. Though the problem is documented as more of a problem in cilantro and less in celery, in severe condition the disease can result in unmarketable produce in any host. The bacteria can be seedborne. However, water from rain, sprinkler irrigation, and heavy dews and fogs will splash bacteria from infected plants onto adjacent healthy foliage resulting in heavy infestation.
To manage the disease, always use tested/treated seeds, rotate crop with non-host to reduce inoculum level, switch from sprinkler to furrow irrigation to limit secondary spread, avoid excessive use of nitrogen fertilizer. If sprinkle irrigation has to be used, use light and more frequent irrigation, or irrigate in the morning or early afternoon so the plants dry off during the day. Copper spray/copper based fungicide provide limited control against the pathogens.
In next few weeks in the Clinic:
Because of the recent increase of Covid-19 related cases in Yuma, the Yuma Ag center is open only in limited capacity. Samples have to be dropped in the bench outside the main building. Please fill out the form provided when you drop samples. Our last day to take samples in the clinic for 2020 will be 18th of December. We will be using the remaining few days of the year to update the lab records, data, and prepare for 2021. Thank you for your love, support, and patience this year.
The Yuma Plant Health Clinic and Plant Pathology program wishes you safe and happy holidays!
In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper.
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).
An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.
Click link below or picture to see the band-steam and co-product applicator in action!
The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address: http://18.104.22.168:460
Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.
VegIPM Update, Vol. 11, No. 7, Apr 1, 2020
Corn earworm: Moth activity decreased during the past 2 weeks and is comparable to what we’ve seen in the past 5 years at the end of the produce season.
Beet armyworm: Moths remain active, and about average for the end of the season.
Cabbage looper: Cabbage looper moths declined in most trap locations over the past 2 weeks. Below average activity for the end of the season.
Whitefly Adult movement at seasonal lows and relatively absent; typical for this time of the season.
Thrips Thrips activity has increased in most trap locations, but still below average for this time of the season.
Aphids: Adults beginning to disperse again; above average abundance for this time of the year.
Leafminers Adult activity increased significantly in Yuma and Gila Valleys; about average for end of the season.
DBM adult captures decreased slightly in most trap locations as crops begin to terminate. The exception is in Bard/Winterhaven where trap catches increased significantly near seed crops. Trap catches overall have been stable during March, but higher than the previous two seasons.
Area-wide Diamondback Moth Trapping Network
In response to the recent outbreaks of Diamondback moth (DBM), Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October 2016. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur in the fall.