Veg Weekly Update and Blog 8/14/2024
All/multiple crops:
Post-tropical storm Debby brought high winds and heavy rain to some parts of eastern NY last week, causing damage to crops and farm structures. A new resource is now available to assist farms in preparing for future weather events, ‘A Guide to Preparing High Tunnels for Extreme Weather.’ This webpage consists of a compilation of advice crowd sourced from regional growers and was prepared by the UVM Extension Ag Engineering team. Note that crops exposed to floodwaters from surface water and crops dropped to the ground by wind should not be harvested due to food safety risks. If you have questions regarding food safety best management practices after an extreme weather event, please reach out to Elisabeth Hodgdon, the food safety lead for the ENYCHP team at eh528@cornell.edu or (518) 650-5323.
As it never seems to fail, we’ve gone from most of the region being dry to now most of the region being saturated and with that comes many of the disease issues that were lying somewhat low! This week Phytophora capsaci, known as P. cap., has really taken off, particularly on farms with a history of it. That, coupled with long, heavy dews has also allowed other diseases like early blight in tomatoes and bacterial leaf spot in peppers to become more active. The age old question of “Should I spray before a rain or wait until it passes” has also come up again. The words of former Cornell University Plant Pathologist Tom Zitter come to mind – it’s better to have it on there before the rain as that is the time you need the protection to keep the disease for getting started or spreading, especially those targeted fungicides. Made sense then and still makes sense.
Alliums:
In the North Country, we’ve been catching leek moth in our traps for the last few weeks. Windowpane feeding damage to leaves and pupae were found in Clinton County on scallions. At this point, farms have harvested their garlic and many onion crops are out of the field, so long season and fall alliums such as leeks are at highest risk for late season damage.
Brassicas:
Alternaria leaf spot in brassica crops is present around the region. Resistance to the fungicide boscalid has been observed this season, leading to recommendations to avoid FRAC 7 fungicides for Alternaria leaf spot management. A new Cornell spray guide “cheat sheet” is in preparation and will be released soon. Organic growers should consider using Oso (polyoxin D zinc salt) at 6.5 fl oz/acre along with an OMRI-listed spreader sticker like Nu Film P or Attach.
Cucurbits:
What is being said the most this week is how early many of the fall ornamentals are this year with many fields planted in the end of May and early June almost fully mature and colored. Here is a link to an article discussing when to know vine crops are mature: Winter Squash and Pumpkin Maturity, Harvesting and Storate Tips. For those that have early markets that’s great, but for many it is too early. The loss of vine cover can lead to sunscald on fruit, especially those with darker colored rinds. This means that you are going to have to be even more diligent in your fungicide applications and you may have to apply 1 or 2 more applications than normal. This week is a good time to use some sulfur with the cooler temperatures and lower humidity levels so that we don’t cause injury. Microthiol Disperss (5 – 10 lbs per acre) is one of the sulfur products that former Cornell Plant Pathologist Margaret McGrath recommended. It can be alternated with chlorothalonil, but only has activity on powdery mildew so if other diseases are a concern like Plectosporium or downy mildew, continue to use the chlorothalonil.
The heavy and prolonged rainy period the last week in a half has allowed Phytophora capsaci to really get started. The Orondis products (Orondis Ultra and Orondis Gold) are still the best choices to use for P. cap. tank mixed with chlorothalonil (Orondis Opti is not labeled for use on P.Cap, but does contain chlorothalonil). However, if the disease is widespread in a field with fruit infection, there is nothing you can do except protect the areas that may not be showing fruit symptoms. Fruit that you harvest that breakdown from P. cap. should not put back in your fields if you can help it. This is true also if you are purchasing fruit from another grower and you suspect P. cap. If you are using Orondis Gold, you are allowed only one application. Other options include Ranman, Omega (also has Gummy stem blight and Alternaria leaf spot on the label), and Zampro.
Nightshades:
Late blight is now present in Spartansburg, PA, Cattaraugus County, NY, and in Aroostook County, ME. The strain US23 has been documented in Ontario, Michigan, Maine, and New York in 2024. This strain is very aggressive on tomato foliage and fruit and on potato tubers. If you believe you have late blight on your farm, please report it to your regional CCE specialist or county office for confirmation so that we may contribute to the national map of late blight infections.
Up until last week tomatoes were looking relatively clean but now early blight can be found pretty easily in many plantings. Look for dark, round spots that enlarge to create a target board appearance on the lower foliage – especially on older plantings that have heavy fruit set or that are ripening. There are quite a few fungicides labeled for early blight but many of them are pre-mixes of multiple products often in different FRAC or families of fungicides so figuring out what to use to reduce the chance of resistance is not easy. Approvia Top (Group 3 & 7) or Quadris Top (also a Group 3 & 7) rotated with Switch (Group 9 & 12) could be a good place to start. Both would need to be mixed with a protectant such as chlorothalonil.
Corn:
Post-tropical cyclone Debby brought corn earworm northwards last week, leading to our first reports of this pest in traps in Clinton County this week. In addition to corn earworm pressure, we are observing high numbers of fall armyworm damage and caterpillars on some farms in the north despite lack of adult moth captures in traps. With low pest pressure earlier the season, growers in the North Country will need to tighten their spray schedules to manage these two pests. As the season progresses and the days and nights get cooler, it will become harder to control CEW in later plantings of sweet corn and the pressure tends to also ramp up so be aware of this for those late plantings.
Although not reported in the region yet, this wet period along with the heavy dews and cooler temperatures could increase the chance of Northern Corn Leaf Blight and Common Rust. There are quite a few fungicides listed for control in the Cornell Integrated Pest Management Guidelines, but be careful – many of the products have different trade names, but have the same active ingredients. Second, be aware that some of the products have a 14-day Pre-Harvest Interval so using them late in the program will be a challenge. The only good news is, most of the products listed have both Northern Corn Leaf Blight and Common Rust on the label.
Tar spot is a new corn disease reported in western NY over the past three years. This season, it is moving closer to the eastern NY region with confirmation of the disease as recently as 7/30 in Monroe County Pa. The small raised black spots with a “tarry” appearance can occur on lower and upper leaves, husks and leaf sheathes. Long dew periods (~ 7 hours of leaf wetness) and high relative humidity favor corn tar spot development in sweet and field corn crops. More information can be found in this article – Tar Spot in Sweet Corn: Be Alert!!
Tar Spot in Sweet Corn: Be Alert!!
Sarah J. Pethybridge, Cornell AgriTech, Geneva, NY; Julie R. Kikkert, CCE Cornell Vegetable Program, Canandaigua, NY, and Darcy E.P. Telenko, Purdue University, Lafayette, IN.
There is a new disease on the block for sweet corn in New York! Tar spot is a fungal disease found first in Indiana and northern Illinois field corn in 2015. It has since spread throughout the Midwest. The disease was found in western NY corn fields every year for the past 3 years, and in central NY last year. Tar spot has potential to severely reduce yields of susceptible corn varieties, so we are closely monitoring disease spread and impact.
In sweet corn, tar spot causes crop loss by contributing to defoliation, reducing ear size, affecting ear shape and
uniformity, reducing processing sweet corn kernel recovery, and decreasing ear marketability through unsightly tar spots on the husks. So far this year, the disease was detected earlier in the season in other parts of the country, and more
recently in Ontario, central Pennsylvania, and eastern Michigan (Figure 1).
Tar Spot Symptoms & ID
The fungus Phyllachora maydis causes tar spot. Disease symptoms are small, raised, black spots that have a ‘tarry’ appearance and occur randomly across upper and lower leaf surfaces (Figure 2). Spots are usually 1/16th to 3/4th of an inch in diameter and typically extend through the leaf so that they can be viewed on both sides. They can also appear on corn husks and leaf sheaths. These black spots are fungal structures that contain spores.
In addition to the black spots, tan to brown lesions with dark borders (‘fisheye’) may also appear around the fungal
structures. Black spots can be mistaken for older common rust pustules (which progress from orange red to black with age) or insect droppings. Insect droppings only appear on one side of the leaf and may easily be scraped off. Tar spots cannot be scraped or washed off and are typically raised from the leaf surface.
Scouting
Tar spot is most likely to be found in fields with a history of sweet or field corn and where corn has been planted in low lying areas and near windbreaks. Consider scouting fields on a weekly basis. The disease will likely first appear in the lower part of the plant canopy in fields with a history of foliar diseases.
Disease Cycle
The tar spot pathogen can survive between seasons on infested sweet and field corn residue left on the surface of the soil. There are also no alternative hosts – the fungus only survives on corn! Tar spot is not seedborne.
Tar spot is favored by growing seasons with high relative humidity (>75%), foggy days, and long dew periods (~7 hours of leaf wetness), just like conditions often experienced across New York! Wind and rain splash disperse the fungal spores. Canopy closure also modifies the environment and makes conditions conducive for the disease. Early disease detection will enable us to plan for subsequent outbreaks and develop protocols for minimizing crop loss.
If you see any suspicious black, tar spots on sweet corn leaves, please notify Sarah Pethybridge (Plant Pathologist, Cornell AgriTech, Geneva; sjp277@cornell.edu; 315-744-5359) or Julie Kikkert (Cornell Vegetable Program;
jrk2@cornell.edu; 585-394-3977 x 404).
