Apr 21, 2021Whitefly Management on Spring Melons 2021
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
With the start of melon season, you will also start seeing seedling diseases on melon. Bacterial fruit blotch (BFB) of melon is a common disease in melon seedlings that can stay in the crop until fruits/seeds are formed. You will be seeing more of this disease in greenhouse transplants.
Bacterial fruit blotch (BFB) of watermelon is caused by the bacterium Acidovorax avenae subsp. Citrulli. The bacteria produceslarge olive green to brown water-soaked lesions on fruit, making them unmarketable.
Symptoms of BFB on seedlings begin with water-soaked areas on the lower surface of the cotyledons and inconspicuous lesions on leaves. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die.
Greenhouse conditions are usually favorable for dispersal and establishment of pathogen. Thus, good greenhouse practices and sanitation is extremely important. Clean transplant trays must be used (disinfect trays if they will be reused) and new soil. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. The bacterium can spread on mist and aerosols. Relative humidity should be kept low through proper watering and good air circulation in the greenhouse. Separate different seedlots, to reduce lot-to-lot spread. Monitor these isolated seedlings daily and destroy trays where symptoms develop. The remaining trays should be sprayed with a labeled bactericide and the applications continued until the plants are transplanted to the field.
The pathogen can be seedborne, so growers should only use seed that has been tested for the presence of the pathogen by a reputable testing facility. Management of BFB includes a combination of preventing the introduction of the pathogen, sanitation to eliminate any inoculum present, and the use of bactericides if the disease appears. There are no commercially available watermelon cultivars that are resistant to bacterial fruit blotch, but there is some variation in susceptibility among cultivars.
Vol. 13, Issue 1, Published 1/12/2022
Last fall, we established two trials investigating the used of band-steam to control Fusarium wilt of lettuce. We utilized the prototype band-steam applicator (Fig 1) described in previous UA Veg IPM articles (Vol. 11 (15) to inject steam into the soil prior to planting. The concept behind band-steam is to disinfest narrow bands of soil using high temperature steam. In the trials, the steam applicator was configured to treat a 4” wide by 4” deep band of soil centered on the seedline.
Experiment results were mixed. At the field site where Fusarium inoculum loads were high, band-steam provided no benefit with virtually all lettuce plants succumbing to the disease (Fig 2a). However, at the trial site where Fusarium inoculum levels were moderate, disease incidence was reduced by more than 40%, and plants appeared to be healthier and more vigorous (Fig. 2b). We’ll be harvesting these plots soon so stay tuned to learn whether these differences translate into significant yield increases.
If you are interested in trying band-steam on your farm, please let me know. We are in the process of constructing a second-generation band-steam applicator that has a higher capacity steam generator and simpler design than our first prototype and are seeking collaborators.
This work is partially funded by the Arizona Specialty Crop Block Grant Program
A special thank you is extended to Larry Ott and Gila Valley Farms for allowing us to conduct this research on their farm.
Fig. 1. Band-steam applicator principally comprising a 35 BHP steam generator mounted on a bed-shaper applicator sled.
Fig. 2. Lettuce seedlings at field sites with (a) very high and (b) moderate levels of Fusarium wilt of lettuce inoculum. Band-steam (left) and untreated (right) plots are shown.
Malva (malva parviflora) is one of the oldest and most pervasive weeds that that we deal with here. It is also known as little mallow or cheeseweed and is in the same family as cotton, okra and hibiscus. It is often classified as a winter annual but survives all year in this region. It has a deep taproot and can grow in compacted clay or sand and in freezing conditions and high temperatures It provides a refuge for insects and diseases that can damage several crops.
Malva is easy to identify both as a seedling and mature plant. The seedlings are distinctively heart shaped and the mature plant is broad and palm shaped. It is very vegetative and can grow to 6 ft.
The deep tap root of this weed makes it difficult to cut out after it is established. Its response to herbicides id somewhat unusual. It is very sensitive to contact herbicides that do not move into the plant. These include Goal, Sharpen Gramoxone , Rely,Aim and others. However, it is not sensitive to systemic herbicides like 2,4-D and Glyphosate. It reproduces from seed and can be controlled preemergence with many of the same preemergence herbicides used in cotton like Prowl or Treflan. The seed pods are wheel shaped which is where the name cheeseweed comes from. Each seed pod contains 10 to 12 seeds