With the produce season essentially finished, it’s time to begin thinking about insect management in melons. Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled. Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when average adult numbers exceed 2 per leaf when averaged across an entire melon field. At this level of adult abundance, immature populations are beginning to colonize. Timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests. This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the feeding disruptors (PQZ and Sefina). For more information on whitefly management and available insecticides, go to these documents on Insect Management on Spring Melons: Whiteflies and Whitefly Control Chart-Spring Melons -2024. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field. If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am).
Though sunflower is not a major crop in Arizona, it is one of the common ornamentals grown in home gardens. We have been witnessing some sunflowers in the area with the disease. It is also important to know about the diseases in sunflower as Arizona is home to large population of wild sunflowers.
Several species of the genus Rhizopus have been implicated in causing head rot, including R. arrhizus A. Fischer, R. stolonifer (Ehrenb.:Fr.) Vuill., and R. microsporus Tiegh. It has historically been considered to be of minor importance, however, it was documented as causing severe losses in Israel, and a recent survey of sunflower diseases in California found that Rhizopus head rot was the most common disease of sunflower. Under favorable conditions, it caused 100% losses in certain field. Infection is initiated in heads through wounds created by hail, birds, or insects.
Symptoms first become noticeable as dark spots on the back of ripening heads, followed by a watery soft rot that later turns brown. As disease progresses, heads dry prematurely, shrivel, and tissues appear to shred. Inside shredded tissues, coarse, thread-like mycelial strands are observed, followed by the appearance of small black dots (sporangia). Sporangia are filled with spores that are easily released and wind-blown to other plants. Symptoms on the flower side of heads include the appearance of mycelium, a grayish, fuzzy substance that is covered with sporangia (Fig 1-7)
Some type of mechanical injury on the head in combination with high temperatures and high relative humidity are required for infection and disease progress. Damage and economic losses are dependent upon time of the season that wounding and infection occurs. Infection rarely occurs before flowering, and greatest yield reductions result when infection occurs before seeds are properly filled. Infection in Israel has been primarily attributed to wounds from bird feeding. In the US High Plains, disease is initiated through head moth infestations and severe storms with hail.
Disease problems can be reduced by controlling the head moth at or before flowering, and by avoiding mechanical wounding after flowering. If you are growing sunflower commercially, it is also important to rogue or control volunteer and wild sunflowers before they produce seed; they may serve as a reservoir for insects and the Rhizopus.
Controlling Disease and Weeds with Band-Steam – Yuma Trials Show Good Promise
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.
Acknowledgements
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.
References
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!
Carryover of Vegetable Herbicides to Wheat Grown in Rotation
Almost all the herbicides used on lettuce, cole crops and melons have restrictions on how soon wheat can be planted in rotation after they have been used. Experience has demonstrated, however, that safe intervals can vary considerably based upon many factors and are almost always much longer than they need to be. The most important factors are rate applied, irrigation practices and tillage. For example, when Kerb used to be banded at 2 to 4 lbs. per acre after planting and incorporated with furrow irrigation, it was common to see treated strips across wheat fields which followed. This is uncommon now that lower rates are Chemigated. We still see some Balan injury at ends of fields or in overlaps especially when sudan is planted. Wheat it not very sensitive to Prefar and carryover injury is uncommon.