It’s not too late to register online or at the door for the 2020 NJ Agriculture Convention & Trade Show. If you haven’t already received a direct mailing from the Vegetable Growers Association of NJ with information about the event, find it on their website at njveggies.org under the convention tab. Membership in the VGA gives you access to 3 days of educational programming, or there is an optional daily pass. The educational program is a collaborative effort of the NJAES/RCE vegetable working group, the blueberry and small fruit working groups, and the new hemp working group. Input and support from NJDA and VGANJ allow us to bring internationally recognized speakers from both our Rutgers faculty and staff, and beyond NJ’s borders to share insights and research on current topics important to NJ agriculture. Thanks to all who have worked to put this program together. We hope to see you in AC.
Vegetable Crops Edition
Seasonal updates and alerts on insects, diseases, and weeds impacting vegetable crops. New Jersey Commercial Vegetable Production Recommendations updates between annual publication issues are included.
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Plectosporium blight caused trouble in cucurbit fields in 2019
Plectosporium blight, also known as Microdochium blight or White speck, caused significant problems in some pumpkin fields last summer in New Jersey. The soil-borne fungal pathogen, although somewhat uncommon, can unexpectedly show up in some years and cause significant losses if left uncontrolled. The fungus survives in the soil on decaying plant debris where it can remain saphrophytic by surviving off organic matter. Infection is characterized by the production of numerous light tan to “bleached” spindle shaped lesions that develop on vines and the undersides of infected leaves. Heavily infected vines and leaves can die leading to premature defoliation and subsequent sunscald on fruit. In cases of heavy disease pressure, spores that are produced on the bottom sides of leaves fall and infect the topsides of fruit laying beneath the canopy. Infection of stems leads to premature browning and drying reduce their longevity. Fruit infection, in most cases, remain mostly cosmetic in nature reducing fruit quality and may predispose fruit to other opportunistic fruit rots. Plectosporium blight often shows up during periods of prolonged wet weather where the soil remains wet for extended periods. “Hot spots” typically appear in fields before the pathogen is further spread by driving rains and wind.
From a production standpoint, stay away from fields with known history of the disease for as long as possible; provide adequate spacing between plants in- and between rows (i.e., avoid the overcrowding of plants); avoid over (preplant) fertilization that can lead to thick, dense canopies; avoid overhead irrigation (if possible); avoid planting in area of a field that remains heavily shaded where soils tend to dry too slow.
Controlling Plectosporium blight begins with regular scouting, recognizing symptoms, and identifying “hot spots” in the field. Protectant fungicides, such as chlorothalonil, as well as those used in weekly maintenance spray programs for cucurbit powdery mildew control will help control Plectosporium blight as long they applied on a weekly schedule with a high volume of water with thorough coverage. To help improve control on the undersides of leaves, a FRAC code 11 fungicide such as Quadris Top or Pristine, can be added to the tank mix. Remember, FRAC code 11 fungicides have translaminar activity and will move from the top surface of the leaf to the bottom. Growers who grow powdery mildew resistant varieties need to remember to scout their fields regularly even if cucurbit powdery mildew has not been detected on the farm or if regular maintenance sprays haven’t begun.
![White speck lesions](https://plant-pest-advisory.rutgers.edu/wp-content/uploads/2013/08/MicroFruit-300x225.jpg)
White speck lesions covering the surface of immature and mature pumpkin fruit. White speck will only cause cosmetic injury to fruit.
![White speck on vine](https://plant-pest-advisory.rutgers.edu/wp-content/uploads/2013/08/White-speck-300x225.jpg)
White speck on vine and stem of infected pumpkin plant. Note the numerous small, white diamond shaped lesions.
Organic Transplant Production: Suppressing Soil-borne Pathogens
Pathogens such as Fusarium, Pythium, Phytophthora, Thielaviopsis and Rhizoctonia that cause pre- and post-emergent damping-off can cause serious problems in organic (and conventional) transplant production. The key to controlling and/or suppressing damping-off pathogens with biological controls is keeping the biological populations high and continually present on root surfaces of the host, and by following good cultural practices. [Read more…]
Controlling basil downy mildew in the greenhouse
Basil downy mildew (BDM) can cause significant losses in the greenhouse. Once introduced into the greenhouse it can be very difficult to manage and eliminate. In the past few years, a vast amount of research has been done on understanding BDM biology and controlling it in the greenhouse using different cultural practices. Before we get to control strategies, let’s review what we know about the pathogen.
First, basil downy mildew is an obligate parasite – meaning it needs a living host to survive. As long as basil is in production in the greenhouse there will be a potential source of inoculum. Sources of inoculum can include fresh intact leaves, but also leaves discarded and fallen on the floor or in an open garbage container. This is important for greenhouse growers who produce basil year round or growers who are looking to extend basil production to later into the fall or earlier in the spring. The simplest method to break the disease cycle would be to stop growing basil for a short period of time and keeping your greenhouse as clean as possible. This would help break the disease cycle by removing the host. Sporangia produced by BDM are short-lived. Without a host their survival is only a few hours to a few days depending on the temperature and environmental conditions. The latent period (the time between infection and symptom development) can range from 5 to 10 days depending on the temperature and environmental conditions. This informs us that plants which appear uninfected may actually be infected without symptom development. Therefore, it is critically important to remove all plants from the operation before restarting production (especially if BDM is already present). A good time to stop greenhouse production (i.e., in the mid-Atlantic region or more northern regions) would be after the first hard freeze in the fall – after the freeze kills all potential sources of inoculum that could come from sources outside the greenhouse.
Control strategies using cultural practices in the greenhouse
Reducing relative humidity in the greenhouse
Basil downy mildew requires high relative humidity (>95%) for 7.5 hrs and at least 4 hrs of leaf wetness for sporulation. Sporulation has been shown to be significantly reduced, or not capable when relative humidity is less than 85%. Thus, maintaining relative humidity below 85% in the greenhouse can significantly help reduce spore production. If this is not possible interrupting the dew cycle (i.e., leaf wetness) with 10 minute periods of drying via fanning/venting every 2 to 4 hours can help reduce spore production.
Control using light
Research has shown that infected plants kept under 24 hours of continual light are unable to sporulate, this was also shown to be temperature-dependent. The type of lighting is also important. Incandescent light was fully inhibitory at 15 to 25oC, but not 10oC. Narrow band LED illumination with red light has been shown to be more inhibitory than blue light. Thus, lighting basil during the night every few hours at short periods of 10 minutes can help reduce sporulation.
Control using fanning and ventilation
Continuous fanning during the night has been shown to dramatically reduce BDM development by reducing leaf wetness (i.e., dew) and reducing relative humidity (keeping it below 95%). Recommendations from Israel are to initiate fanning when relative humidity reaches 70% in the greenhouse and to stop it when it is below 60%.
The key to controlling and mitigating BDM development in the greenhouse is controlling relative humidity and periods of leaf wetness to help reduce potential sporulation. Using a combination of cultural practices mentioned above can help reduce BDM development, but it will come at a cost to you in the form of additional hardware, temperature and relative humidity monitoring equipment and the cost of electricity. The first step in this process involves understanding where the initial source of inoculum may be coming from. Evidence for BDM being seed-borne is mixed. During the spring-summer-fall, greenhouse basil production will always be at-risk from infections coming from an outside source, including diseased seedlings you may be purchasing. Successfully breaking the BDM disease cycle (without the use of chemical inputs) in greenhouse operations has limited opportunities (e.g., in northern regions where freezing weather occurs). This can only occur in the fall, after freezing weather which can kill all outside sources of inoculum and by not carrying over infected plant material into the winter season, thus the need for a basil-free period during the production cycle. This is especially important in small greenhouse operations that produce basil organically or without the use of chemical input.
These management practices should significantly reduce your BDM problems though will require more of your attention and potentially additional equipment and supplies. Coupling best management practices with new downy mildew resistant basil varieties will further provide protection to you. Try the new basil downy mildew resistant varieties including Rutgers Obsession DMR, Rutgers Devotion DMR, Rutgers Passion DMR, and Rutgers Thunderstruck DMR or other DMR resistant sweet basils such as Prospera, and see which ones work best for you.
For information on Rutgers DMR sweet basils, where to purchase seed, as well as control strategies, and ongoing research efforts please follow the Rutgers basil downy mildew breeding program on Instagram at #Rutgersbasil.
Resources:
Tracking basil downy mildew in the US
Fungicides for the control of BDM
Controlling basil downy mildew in the greenhouse
Authors: Andy Wyenandt and Jim Simon, Department of Plant Biology, Rutgers University
Understanding Protectant Fungicides
(FRAC groups M01 – M11)
Protectant (contact) fungicides, such as the inorganics (copper, FRAC group M01) and sulfur (FRAC code M02); the dithiocarbamates (mancozeb, M03), phthalimides (Captan, M04), and chloronitriles (chlorothalonil, M05) are fungicides which have a low chance for fungicide resistance to develop. Protectant fungicides typically offer broad spectrum control for many different pathogens.
Why wouldn’t fungi develop resistance to protectant fungicides? Protectant fungicides are used all the time, often in a weekly manner throughout much of the growing season.
Got humidity in the greenhouse? Get rid of it!
Unfortunately, closed greenhouses retain heat and unwanted humidity which can spell problems if left unchecked, especially during prolonged periods of overcast days and cooler weather.
Remember, high relative humidity equals wet leaves which can favor the development of diseases such as Botrytis or bacterial diseases such as bacterial leaf spot. To avoid potential problems, do your best to vent out as much humidity as possible on a daily basis in the early morning or late afternoon. Turn on circular fans to promote air movement and finish watering earlier enough in the day so leaves have enough time to dry out before nightfall. Any flats with transplants with suspect leaf spots should be pulled out of the production facility and isolated until a proper diagnosis can be made.
As a side note, stressed transplants where water and/or fertility have been withheld are also more prone to disease development. A light fertilizer application may go a long way in improving transplant health before setting in the field.
Please see Table E-14 in the upcoming 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations guide for a list of control options for important diseases in greenhouses.