The weather this spring has been anything but normal with the up and downs in the temperature as well as the on and off again sunny days followed by many days of cloudy weather. These types of weather patterns can cause problems in transplant production in the greenhouse, especially when it comes time for watering. Hot days may require more than one watering, and cloudy days may require no water. In either case, growers need to anticipate their transplant water needs without over or under estimating watering. Of course, other factors include the growing media and the plant itself. Lets focus on media, for example, growers using a lighter soilless media, these will dry out much quicker than a heavier media and will require more daily watering (e.g., once in AM, afternoon, and evening). Growers using a heavier media may only have to water once a day, or early in the AM and maybe once more in the PM. Either type of media works fine as long as the weather doesn’t change and it fits the growers needs. Proper transplant watering is all about adjustment. If you have stuck to the same daily watering schedule this spring its very likely you have grossly over or under watered your transplants at some point. And, in all likelihood, grossly over or under watered trying to correct the situation. Uniformity is also key when it comes to proper transplant watering. If you find yourself spot watering out of schedule because some flats dry out quicker than others then most likely your uniformity is off. This is easily done when watering is done by hand with a wand. Poor uniformity can also be the result of transplant flats being set on uneven benches or uneven floors. Much like a field, low spots tend to collect the most water. All of this can lead to uneven transplant growth as well as disease and pest pressure, such as fungus gnat problems. If you are experiencing uneven transplant growth, then most likely your watering is uneven. For transplant growth to remain even, flats need to be watered each time to maximum water holding capacity, where each cell in the flat holds the maximum amount of water. An easy way to see this is to watch for water dripping out the bottom of the flat. As important, flats should also uniformly dry out. Below is an example of tomato transplants that have been pulled from the same flat. You can see the differences in plant height as well as root system formation as a result of uneven watering in a “heavy” soilless media. Cells that have remained on the wet side show poor growth and poor root system development because of a waterlogged cell; whereas cells that have been receiving the appropriate amount of water have much better growth and a nice root ball. The weight test. When was the last time you picked up a transplant tray? Picking up a transplant flat every once in a while will give you an idea of how well your watering schedule and uniformity is! Everyone has picked up a tray that has felt like it has the weight of a rock or the tray breaks apart because of the weight, or when you pick it up and it feels as light as a feather. Doing this is a good way to determine if your soilless media is “heavy” – holds more water than you think or if you have been overwatering on days you shouldn’t be or if you have not watered enough. Consistency is key when watering. Going from an extremely wet to an extremely dry transplant tray is not what you want for the transplant production season. You want consistent soil moisture as much as possible, thus proper transplant watering is all about the proper adjustments and knowing your media.
Understanding phenylamide (FRAC group 4) fungicides
The phenylamide fungicides (FRAC group 4) are a highly active class of fungicides that target oomycete pathogens such Phytophthora and Pythium spp. FRAC group 4 fungicides are also highly effective against downy mildew pathogens such as Pseudoperonospora cubensis (cucurbit downy mildew), Phytophthora infestans (Late blight), and basil downy mildew (Peronospora belbahrii) and many other important pathogens in vegetable production. Like other fungicide classes, FRAC group 4 fungicides have a high-risk for fungicide resistance development. The phenylamides (PA) inhibit ribosomal RNA (rRNA) biosynthesis in oomycete pathogens which inhibits several life stages in oomycetes including hyphal growth, haustoria and sporangia formation. The exact mechanism for resistance is not completely understood although research has shown that PA resistance is control by a single incompletely dominant gene although multiple mutations or mechanisms may be involved in PA resistance development. Pathogens such as cucurbit downy mildew, late blight, and basil downy mildew can be disseminated over vast geographic distances in any given year, thus this migration can be responsible for the introduction of new pathogen genotypes (including PA resistant) to new locations along with local selection pressure due to PA fungicide use resulting in changes in the pathogen population. Additionally, pathogens such as P. infestans and P. capsici (Phytophthora blight) are highly sexually active at the local level, because of the potential presence of two mating types (A1 and A2), you have a “recipe” that is always evolving. Resistance development to PA fungicides is often described as sensitive, intermediate, or resistant based on EC50 (Effective Concentration) values of the different fungicides needed to kill 50% of the pathogen in laboratory assays. This type of collected information is useful in determining what proportion of a given local, or wide geographic pathogen population, may be PA resistant. Recommended resistance management guidelines developed FRAC have not changed since 1997and are intended as general recommendations that must be adapted to respective pathosystems, fungicide use and patterns, and resistance levels.
The following are general recommendations for PA fungicide use as stated by FRAC.
- PA fungicide should be used on a preventative basis; and not used as a curative or on a eradicative basis
- As foliar applications, PA fungicide should always be tank mix with a unrelated fungicide from a different FRAC group
- The total number of PA applications per season should be limited to 2 to 4 depending on label requirements
- PA sprays are recommended for use earlier in the production season during active vegetative growth
- PA should not be used as soil treatments against foliar disease development
Resistance development in P. capsici to mefenoxam has been known for many years in southern New Jersey. This is most likely to the widescale and overuse of mefenoxam in its early days because of the lack of an alternative chemistry, as well as a result of crop rotations where susceptible crops were planted in the same field for many years. In the past decade, there have been several new fungicides from different FRAC groups labeled for oomycete control. These include: Orondis Gold (oxathiapiprolin + mefenoxam, FRAC groups 49 + 4), Previcur Flex (propamocarb, 28), Ranman (cyazofamid, 21), Presidio (fluopicolide, 43), and Phosphites (33) for field use. Ranman, Previcur Flex, and phosphites have greenhouse use labels for Pythium control. Ranman and Previcur Flex can be applied in the transplant water. Orondis Gold, mefenoxam, metalaxyl, and the phosphites are the most systemic of the group and should readily be taken up the by plant via application through the drip. Presidio has locally systemic and translaminar activity and offers protection of the root system via drip. Ranman has protectant-like activity and thus will offer root system protection. Growers with a known history of mefenoxam-insensitivity on their farm should use Presidio, Previcur Flex, or Ranman plus a Phosphite fungicide in rotation in their drip application programs. Importantly, if mefenoxam has not been used in particular fields on any crop for a number of years (more than 5+) the fungus may revert back to being mefenoxam-sensitive and control with these products may return.
For more information please see specific fungicide labels, crops sections, and greenhouse uses in Table E-11 in the 2020/2021 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Reference:
Hermann, D.C., McKenzie, D., Cohen, Y., and Gisi, U. 2019. Phenylamides: Market trends for resistance evolution for important oomycete pathogens more than 35 years after product introduction (FRAC code 4). Chapter 6 in: Fungicide Resistance in North America, 2nd Ed. Katherine L. Stevenson, Margaret T. McGrath, and Christian A. Wyenandt (eds). The American Phytopathological Society, St. Paul, MN.
Additional resources:
Damping-off: Identifying and Controlling Early-Season Damping-off Pathogens
Understanding Damping-off Pathogens During Seeding and Transplanting
Damping-off: Identifying and Controlling Pathogens in Transplant Production
It is extremely important to know which pathogen is causing damping-off problems and which fungicide to properly apply. The key to controlling damping-off is being proactive instead of reactive. Always refer to the fungicide label for crop use, pathogens controlled, and application rates.
Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off). Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia and Fusarium spp.
Control of damping-off depends on a number of factors. First, is recognizing the conditions which may be leading to the problem (i.e., watering schedule/greenhouse growing conditions) and second, identifying the pathogen causing the problem. Reducing the chances for damping-off always begins with good sanitation practices prior to transplant production.
Conditions Favoring Damping-off
Although all four pathogens are associated with damping-off, the conditions which favor their development are very different. In general, Phytophthora and Pythium are more likely to cause damping-off in cool, wet or overwatered soils that aren’t allowed to dry out due to cloudy weather or cooler temperatures. Conversely, Rhizoctonia and Fusarium are more likely to cause damping-off under warmer, drier conditions especially if plug trays are kept on the dry side to help reduce transplant growth. [Read more…]
Understanding Damping-off Pathogens During Seeding and Transplanting
Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production and early-spring. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off). Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia and Fusarium spp.
It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply.
Understanding root rots in fall-seeded and transplanted crops
Damping-off is caused by a number of important vegetable pathogens and is very common at seeding and transplanting in spring and fall. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off) or soon after transplanting. Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia, and Fusarium spp.
It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply.
Understanding Damping-off Pathogens in Transplant Production
Damping-off is caused by a number of important vegetable pathogens and is very common during transplant production and early-spring. Damping-off can kill seedlings before they break the soil line (pre-emergent damping-off) or kill seedlings soon after they emerge (post-emergent damping-off). Common pathogens that cause damping-off include Pythium, Phytophthora, Rhizoctonia and Fusarium spp.
It is extremely important to know which pathogen is causing the damping-off problem and which fungicide to properly apply.