Feb 7, 2024Keep an Eye Out for Corn Earworm in Spring Head LettuceTo contact John Palumbo go to: jpalumbo@ag.Arizona.edu
With melon season on full bloom, you will also start seeing diseases on melons. Cucurbit yellow stunting disorder is more of a problem on fall melons but they can also occur in summer melons. Cucurbit yellow stunting disorder is a cucurbit disease caused by a plant virus named Cucurbit yellow stunting disorder virus (CYSDV; genus Crinivirus, family Closteroviridae). This virus was first detected in southern California and Arizona in 2006 and infects cantaloupe and honeydew melon, watermelon, and various types of squash. CYSDV is transmittedexclusively by the whitefly, Bemisia tabaci. Symptoms always start from the oldest leave which is a diagnostic feature of the virus.
All biotypes of B. tabaci known to exist in North America can transmit the virus efficiently, including biotypes A, B and Q. Whitefly transmission is responsible for virus spread over short distances (e.g., within and between fields). However, with high winds whiteflies can move long distances and transport the virus. The virus can stay infectious within whiteflies for up to 9 days. As virus infection is systemic (meaning they have to be circulated inside the plant system to show symptoms) it can take 3 to 4 weeks for disease symptoms to develop following infection. This gives a window for infected symptomless plants can be unknowingly transported and can lead to epidemics. The virus is not transmitted mechanically (by touch, mechanical damage, cuts etc) or via seed. However, the virus can be efficiently transmitted even if there is low whitefly pressure in the field.
The best management approach is to monitor the whitefly population and be proactive with insecticides application. Rotate insecticides with different modes of action Group numbers to minimize development of insecticide resistance. Practice good weed management in and around fields to the extent feasible. Remove and destroy old crops/volunteers, enforce regional cucurbit -free period to eliminate the virus from the cropping system.
Sweet Shield and Novira varieties seem to do well in Yuma area.
A technique that I’ve been curious about for some time now to minimize the number of weeds close to crop plants is the use of early (seedling stage of growth) close cultivation. Early close cultivation can be accomplished using a camera guided cultivator equipped with specially designed cultivating tools. Examples of the technology and technique were demoed at our 2016 and 2022 AgTech Field Days by K.U.L.T.-Kress, LLC1, the manufacturer of the equipment. The systems basically comprised a camera vision system for tracking the crop row, a toolbar attached to a parallel linkage that facilitated side-to-side movement and small cultivator assemblies for each of the seedlines (Fig. 1). In the demos conducted in lettuce, cultivating tools were positioned such that the uncultivated band was only about 2” wide (Fig. 2). If the crop were thinned by hand hoe or chemically, only a small area (roughly 2” x 2”) around the keeper plant would remain that had not been cultivated or treated with an herbicide material (Fig. 3). Assuming that existing weeds were controlled, and no new weeds emerge, the number of weeds close to the crop plant would be minimal. I realize soil disturbance near the crop plant is not desired but cultivating 1” away from seedling lettuce should be comparable to, and not cause any more crop injury than thinning seedlings spaced 2” apart with a hand hoe. I’m curious what your thoughts are on this. I’d love to hear your feedback.
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Fig. 1. K.U.L.T.-Kress camera guided cultivator (a) equipped with cultivating tools
designed for close cultivation (b). (Photo credits: Mazin Saber, University of
Fig. 2. Close cultivation of seedling lettuce with a camera guided
cultivator. Close up view (a) and far view (b). (Photo credits: Mazin Saber,
University of Arizona)
Fig. 3. Close cultivation of seedling lettuce with camera guided
cultivator leaves a roughly 2” wide uncultivated band around the
seedline (a). Thinning by hand hoe or chemically would kill plants in the
seedline (red shaded area) and leave a small area (roughly 2” x 2”)
(indicated by white box) around the keeper plant that had not been
cultivated or treated with an herbicidal material (b). Assuming no new
weeds emerge, the number of weeds near the crop plant that are
difficult and time consuming to remove is minimal.
Fig. 4. Video of camera guided cultivator equipped with cultivating tools
designed for close cultivation operating in six-line seedling romaine
lettuce. Click here or on the image to see the video. (Video credit: Mazin
Saber, University of Arizona)
The subject of Prefar (bensulide) residue in the soil and waiting period before spinach was was brought to the IPM team in the past. Inadvertently some sections of fields with bensulide residue could be scheduled for planting spinach too soon. The rotational crop instructions on the label say: “All other crops should not be planted for 120 days and the soil must be tilled to a minimum of 4 inches prior to replanting”. The Section VI of the PCA Sudy Guide recommends 4 months recropping interval for Alfalfa, wheat and Cotton.
The site Gowan.com explains specifically: “Do not use Prefar 4-E on spinach or Swiss Chard as severe phytotoxicity will occur”1.
We also heard different opinions, some minimizing the persistence on this herbicide in fine textured soils. So, we tried it in our clay soil at the Yuma Ag Center with a 40% Clay, 38% Sand, and 22% Silt.
After a bensulide lettuce evaluation was completed, we reworked the beds and planted spinach. This was done 45 days after treated.
Here’s how the stand was affected:
Figure1. Effect of bensulide herbicide residue in spinach stand. Broadcast “DI” means delayed incorporated and “II” Immediately incorporated with sprinkler irrigation.
Additionally, leaves, roots and plant lengths were evaluated showing vigor reduction in treated plots.
Figure 2. Bensulide effects to spinach stand 45 planted 45DAT.