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New photo gallery: Anthracnose in cucurbit crops

Anthracnose occurs occasionally in cucurbit crops in the Northeast.  Following pictures of cucumber leaves taken on 7 and 15 August in 2014 show how symptoms can change in appearance in just one week.  The circular leaf spots are initially water-soaked, then become yellow to tan.  Round, black, sunken spots can develop on fruit.  On fruit spots the pathogen produces diagnostic salmon-colored spores under moist conditions.

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View photo gallery.

New photo gallery: Fusarium crown rot and fruit rot of pumpkin

fusarium-pumpkin5x640The fungus Fusarium infects crown, root, and fruit tissue of pumpkin.  Symptoms have been observed on Long Island in fields where there is limited rotation, such as those used for u-pick, suggesting that it takes time for pathogen population to increase to a damaging level.

It is important to distinguish Fusarium crown rot from Phytophthora blight because conventional fungicides with targeted activity against Phytophthora are not effective against Fusarium.  Plants wilting and dying from Fusarium crown rot are rotten at the crown area extending downward into the main root, internal tissue is yellow to orange while plant tissue infected by Phytophthora is collapsed, dark on the outside and inside, and occurs at the crown and further up on the vine with the roots often not affected.  Fusarium crown rot tends to affect plants scattered throughout a field while Phytophthora blight is more often in areas where soil water drainage is poor.  Both pathogens can survive in soil for years. 

Continue to photo gallery

Disease Alert: Spinach downy mildew

The ‘Late blight’ of Spinach Developing Now in Northeast. See It?  Report It!  Manage It!

Downy mildew has been found recently in spinach at several farms in the northeastern U.S.  This devastating disease has not been confirmed in the region for several years, thankfully as it has been a major production constraint in California.  Pathogens causing downy mildew are Oomycetes and thus are related to the late blight pathogen.  They are similar in ability to produce an abundance of wind-dispersed spores capable of moving long distances and to not need leaves to be wet to infect (high humidity is sufficient), plus ability to devastate crops. 

All growers with spinach should inspect their plants for symptoms promptly NOW and also in spring plantings to catch if there is carry over or new outbreaks.  If downy mildew is suspected, please contact your local extension specialist and send an e-mail to mtm3@cornell.edu.

It will be CRITICAL that all high tunnel and overwintering spinach crops with downy mildew be destroyed couple weeks before the start of the spring spinach production season in the region to avoid carry over into 2017.

Purplish-gray, fuzzy growth on the underside of leaves. Click for larger view.

Purplish-gray, fuzzy growth on the underside of leaves. Click for larger view.

Symptoms.  Purplish-gray, fuzzy growth of the pathogen, which is usually on the underside of leaves, is diagnostic.  Early morning is the best time to see as the growth (which is spores and the structures holding them) is produced overnight, then during the day the spores are dispersed.  On the top side of leaves, opposite where the growth develops, the leaf tissue will be yellow, initially dull becoming brighter and larger with time.  Subsequently affected tissue will become dry and tan.  If only leaf yellowing is seen, which could occur when humidity is low, put suspect leaves upside down on wet paper towel in a closed ziplock bag for a day.  Keep the bag in the dark, such as inside a box, to further promote the pathogen if present to develop.

Management.   Resistant varieties have been an important management practice, but the pathogen has proven adept at developing new races able to overcome host resistance.  Last year race 16 was discovered.

Yellowing leaf tissue on top side of leaves opposite the fuzzy growth underneath. Click for larger view.

Yellowing leaf tissue on top side of leaves opposite the fuzzy growth underneath. Click for larger view.

To maximize success of control with fungicides, start early in disease development (preventive best), and apply weekly.  Conventional fungicides for this disease include: Actigard, Aliette, Merivon, Quadris and other QoI fungicides, ProPhyt and other phosphorous acid fungicides, Ranman, Reason, Revus, Ridomil Gold, and Tanos.  Downy mildew is difficult to manage with organic fungicides based on experience of researchers and growers in CA.  Labeled products include copper, Actinovate, Double Nickel, Regalia, Oxidate, Trilogy, and Zonix.  Copper is considered most effective but based on few evaluations of organic products.  Check REI and PHI when selecting conventional or organic fungicides to make sure fits production schedule.

Note that while leaves are held in plastic bag after harvest, affected leaves may rot and new symptoms may develop, especially if there is residual moisture from washing.

Promptly destroy infected, abandoned crops to eliminate this source of inoculum for other plantings in the region.  The pathogen can survive a few years in soil when both mating types are present together enabling production of oospores.

Other Susceptible Plants.  The pathogen, Peronospora farinosa f. sp. spinaciae, is only known to infect spinach.  It is possible some Chenopodium weed species are susceptible to some races.

Pathogen Sources.  It is possible contaminated seed or infected spinach produce from outside the region was the source of the current outbreak.

Favorable Conditions.  Cool with high humidity.  Optimal temperature range for this pathogen is 59 – 70 F.

Margaret Tuttle McGrath
Plant Pathology and Plant-Microbe Biology Section, SIPS, Cornell University
Long Island Horticultural Research and Extension Center
3059 Sound Avenue, Riverhead, NY 11901; mtm3@cornell.edu

Please Note: Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.  The specific directions on fungicide labels must be adhered to — they supersede these recommendations, if there is a conflict.  Check state registrations and labels for use restrictions.

Prepared 11/14/16

Does Your Basil have Downy Mildew?

From Margaret McGrath (mtm3@cornell.edu), reposted from CCE Suffolk Long Island Gardening (2016-09-16):

If your basil leaves have turned yellow and display a dark-brown sooty growth on their underside, then your plants have downy mildew, a regularly occurring disease on Long Island since it first appeared here in 2008. Click on the photo gallery on my Vegetable Pathology – Long Island Horticultural Research & Extension Center webpage to look at pictures of diseased basil to help determine if your herbs are affected.

Basil downy mildew. Click image for larger view.

Basil downy mildew. Click image for larger view.

There’s also lots of information about basil downy mildew on my webpage at Cornell Vegetable MD Online. If you’d like to log a report of your diseased basil to help me with a study on basil downy mildew, click here at Basil Downy Mildew Monitoring Records 2016. And for a national perspective about where it has appeared in the United States, visit Where in the USA is Basil Downy Mildew? This is a good web reference to visit in the future to learn when other gardeners are starting to find the disease on Long Island and elsewhere, too.

Downy mildew is hard to manage in basil plants. My recommendation for gardeners is to grow basil in pots and not expose them to high humidity (above 85%) which the pathogen requires to be infectious. Low humidity can be maintained by keeping plants indoors overnight and on rainy days. For more information, visit my webpage How Gardeners Can Manage Downy Mildew in Basil

Starting in late July, I grow my second planting of basil in pots because downy mildew typically begins developing for me on Long Island during August. Also, since basil is very cold sensitive, bringing plants into a warm house overnight maintains basil quality when night temperatures start dropping to below 55F.

If your basil is still green and healthy, consider yourself lucky and go knock on wood! And then drop me an e-mail. Cheers!

Dr. Meg McGrath is Associate Professor at Cornell University’s Long Island Horticulture Research and Extension Center in Riverhead, New York, where she conducts research and extension activities to help farmers manage diseases.

New photo gallery: Potato Virus Y

pvy

Symptoms caused by Potato Virus Y (PVY) vary quite extensively in appearance and also severity, from negligible to severe.  This is due to the strain (type) of PVY causing the infection and the potato variety.  PVYNTN is now the dominant of the 3 PVY strains occurring in the USA.  Its presence has resulted in this disease re-emerging to become a serious problem in the USA.  This is partly because PVY is difficult to detect in many varieties because of very mild symptoms.   Consequently PVY is difficult to detect in seed potato fields.  This was not the case before 1990 when the ordinary strain (PVYO) occurred.

Continue to photo gallery.

New virus of tomatoes (and other crops)

There is a new virus that I want you to be aware of.  TCSV (tomato chlorotic spot virus).  It is related to TSWV and INSV (all tospoviruses), sufficiently closely that a plant with TCSV can falsely test positive with an immunostrip assay for one of the others.  Symptoms are similar.

I have an article plus photos posted at the Vegetable MD Online website: Tomato Chlorotic Spot Virus: New Virus of Concern for Several Crops

Please let me know if you see virus symptoms especially on tomato.  I have a colleague studying TCSV who is eager for possible samples.

TCSV Photograph courtesy from: Dr. Shouan Zhang, Tropical Research & Education Center, University of Florida

Photograph courtesy from: Dr. Shouan Zhang, Tropical Research & Education Center, University of Florida

New photo gallery: Cucurbit powdery mildew

Powdery mildew is the most common and widespread disease of this large, diverse crop group occurring in both field and protected-culture (greenhouse) crops.  White, talcum-like, powdery fungal growth develops on both leaf surfaces and on petioles and stems. Symptoms usually develop first on older leaves, shaded lower leaves, and lower leaf surfaces. Powdery spots on lower surfaces may have yellow spots opposite on the upper leaf surface. Field-grown plants become susceptible when producing fruit or stressed. Infected leaves and then plants senesce prematurely. Rarely infection occurs on immature fruit of watermelon, gourd and cucumber. Read more and visit photo gallery.

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Are you damaging your vegetable garden soil?

From Margaret McGrath (mtm3@cornell.edu), reposted from CCE Suffolk Long Island Gardening (2016-04-26):

The rototiller is a popular tool used by home gardeners to control weeds, incorporate fertilizer and lime, and loosen up the soil for planting. While valuable for some purposes, it is important to recognize that rototilling does have a dark side: Earthworms and soil microbes, important for good soil health, are damaged by it. And organic matter in the soil is broken down and lost.

Farmers have learned about the negative impacts of rototillers and other tillage tools they regularly use. Today many are adopting “reduced tillage” practices to protect their soil. Cornell Cooperative Extension agriculture staff are working with Long Island farmers to help them change these practices successfully.

Since I work with farmers and CCE agriculture staff, I understand the importance of good soil health. So I decided to implement what I learned at work in my home vegetable garden, pictured below. I am excited about how my garden soil has improved. Its organic matter has increased, there are a lot more earthworms, and the soil is very friable, which makes it easy to dig holes for transplanting.

Here is what I do now to protect soil health. First, I rototill only where I am directly seeding, which is currently just peas. I used to have my husband till the whole garden each spring with our big hand rototiller. Now we use a small rototiller to prepare our rows for the peas, tilling only the soil where I plant seeds and not disturbing the walkways between these rows.

pea-bedx640

My tilled seedbed for peas with undisturbed paths between beds.

Peas and path later in the season.

Peas and path later in the season.

Second, I cover the vegetable garden with shredded leaves and fresh grass clippings from the rest of the yard. This provides excellent weed control, so I don’t need to use the rototiller for controlling weeds. And this free mulch is a good source of organic matter that earthworms digest and move into the soil. I have a bagging, mulching lawn mower for collecting material for this ground cover. I just rake the mulch out of the way when I plant. I use a chipper-shredder to turn last year’s dead flower stalks and ornamental grasses into straw mulch to place around the base of the vegetable plants.

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My garden mulched with grass clippings.

Third, I use a trowel or shovel to dig holes for transplanting, depending on seedling size. Often I put homemade compost and/or a little granular fertilizer in the hole, and mix this into the soil with a scratcher. Not turning over an entire row of soil when I transplant helps preserve the soil’s organic matter and improves its water retention, which is great for soil microbes and my vegetables.

Tomato and Potato Late Blight: What to do NOW!

From Margaret McGrath (mtm3@cornell.edu), reposted from CCE Suffolk Long Island Gardening (2016-06-06):

late blight-resistant Jasperlate-blight susceptible SunGold
Late blight-resistant tomato variety Jasper (left) and susceptible SunGold (right) severely affected by late blight.  Both images taken on 9 Oct 2013 in my garden. Click images for larger view.

Late blight is arguably the worst problem that can appear in a vegetable garden! Its highly contagious and very destructive nature means everyone growing susceptible tomato and potato plants – gardeners and farmers alike – needs to take action to prevent late blight from occurring and needs to respond quickly when it appears. The major epidemics of this disease on Long Island in 2009 and 2011 are thought to have started with just a few infected plants.

Early Season Action Steps to Prevent Late Blight:

  • Select varieties that have resistance to late blight. For example, the popular SunGold cherry tomato is susceptible to it; Jasper cherry tomato is not. Find more information about resistant tomato varieties at the eXtension website.
  • Plant certified potato seed. Do not plant potatoes from last year’s garden or from the grocery store. There is a higher probability for the late blight pathogen (Phytophthora infestans) to be in “table-stock” potatoes.
  • Destroy any potato plants that grow as “volunteers” in compost piles or in the garden from potatoes not harvested last year.
  • Inspect tomato seedlings carefully for symptoms before purchasing them. The pathogen as it exists in the United States is not known to survive in tomato “true” seed and then infect the seedlings, so if you grow your own seedlings, late blight is not a concern until they are planted. Seedlings become infected by growing near other affected plants.
  • Become knowledgeable about the different symptoms of late blight and its imitators. I have posted more photographs of late blight on tomatoes and on potatoes.
  • Monitor the occurrence of late blight in the United States at usablight.org. You can sign up on that website to get an alert by text or e-mail when a report has been logged nearby, so you can be one of the first to know when late blight has been found on Long Island.
  • Inspect your tomato and potato plants for symptoms at least once weekly.
Inspect tomato plant leaves for early symptoms of late blight, such as the discoloration shown here. And then act fast!

Inspect tomato plant leaves for early symptoms of late blight, such as the discoloration shown here. And then act fast!

What to do when late blight symptoms are found:

Immediately call our Horticulture Diagnostic Lab at our hot line at 631-727-4126 from 9 a.m. to noon, Monday through Friday. Alice Raimondo and Sandra Vultaggio, our Horticulture Consultants, can help determine whether you do, indeed, have late blight, and answer questions about proper handling of an outbreak. (Elsewhere in New York, contact your local office of Cornell Cooperative Extension. Outside New York, find local contact here.)

Best management steps for dealing with disease are based on knowledge of the pathogen’s biology and life cycle. The late blight pathogen in the United States is not known to reproduce sexually, as it does elsewhere in the world including in parts of Europe. Where it does reproduce sexually, it produces a type of spore (oospore) that enables the pathogen to survive in true seed and in soil; consequently, rotation is an important management step in Europe, but this is not necessary for controlling late blight in the United States.

New photo galleries: Lettuce Crown Girdling, Potato Blackleg Caused By Dickeya

We just added two new photo galleries from problems detected this spring:

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