Phytopthora Blight  
Cover crop trial at Phytophthora Blight Research Farm



There is no one fool-proof strategy that will protect susceptible crops from Phytophthora blight. Instead, managing this disease requires an effective integration of numerous techniques.

Keeping Phytophthora blight out

Infected Plants

If you already have Phytophthora blight


Soil & Plant Health

Chemical Control

Map of Counties Where Phytophthora Blight Has Either Been Confirmed or Reported ("Potential")

Keeping Phytophthora blight out (printable fact sheet)

The first line of defense against Phytophthora blight is to keep it out of your fields or garden. If you haven’t yet seen Phytophthora blight in your vegetables, being vigilant about what goes into your fields can help protect your vegetables. The good news is that Phytophthora blight is not blown long distances by the wind. But, it can be spread in infested soil and water, or infected plants (see How does Phytophthora blight spread?).


Infected plants.
Culled fruit and rogued plants that might be infected with Phytophthora blight should never be dumped into production fields; send them to the dump in plastic bags, bury them deeply in non-cultivated soil, or burn them, instead.


Infested soil.
The soil that clings to your shoes or tractor tires can be harboring thick-walled overwintering spores of Phytophthora blight (read more here). If some of your fields have Phytophthora blight, but others do not, wash your equipment between fields, or work infested fields last to prevent moving spores into “clean” fields. In at least one instance, Phytophthora blight was brought onto a farm in vermicompost from worms which were fed infected fruit. The overwintering spores of Phytophthora blight are not destroyed by the digestive system of a worm, and they will likely not be killed by temperatures reached in home compost piles. When you purchase compost for your field or garden, be sure you know how it was produced and that it was sufficiently heated during production.


In 2008, a small survey of irrigation water around New York State found Phytophthora blight in all surface irrigation sources tested (but not in wells) by the end of the growing season (see map below). If spores of Phytophthora blight get into your irrigation source, you may be inoculating your crops, every time you irrigate. More research is needed on how to kill P. capsici spores in irrigation water, but knowing where your irrigation water comes from is an important first step. Does run-off from your fields or someone else’s fields drain into your irrigation source? Have there been signs of Phytophthora blight in these fields?

Map of Irrigation Water Sample Sites

Irrigation Water Sample Sites



If you already have Phytophthora blight (printable fact sheet)

If Phytophthora blight is already in one or more of your fields, do not despair! There are many steps you can take to limit losses from this disease, including: planting tolerant varieties, rotating to non-susceptible crops, and maintaining appropriate moisture levels in the field.


Tolerant varieties
Some sweet pepper varieties and a few hot pepper varieties are tolerant to infection by Phytophthora blight (click here for a list of varieties we've tested in New York). The water mold which causes Phytophthora blight (Phytophthora capsici) is a very diverse organism, so different vegetable varieties may respond differently to the particular strains of Phytophthora blight you have in your field.Unfortunately, there are currently no cucurbit varieties with any tolerance to Phytophthora blight. More work needs to be done in this area.


Good drainage
Because Phytophthora blight thrives when lots of moisture is around (read more about the biology of Phytophthora blight), anything you do to make sure that your vegetables have the right about of moisture, but not too much, can reduce losses to Phytophthora blight. Take steps to improve drainage in your field, and plant peppers, tomatoes, eggplants, and bushing cucurbits on raised beds that are at least 6-8 inches high. Vining cucurbits should not be planted on raised beds, unless you are prepared to move each fruit out of the “troughs” between the rows and onto the top of the bed. Be careful not to over-irrigate.

Although the overwintering spores of Phytophthora blight can survive in the soil for years, every year you rotate an infested field to a non-host crop will reduce the number of spores that survive to the following year. But, be careful! Some weeds can also be hosts of Phytophthora blight (see host list), so careful attention to weed control throughout your rotations is important.


Although not always feasible, when you first see Phytophthora blight begin to infect plants in a field, you can slow the spread of the disease by removing the symptomatic plants and a “buffer zone” of healthy plants around the sick ones. Each plant that becomes infected can produce millions of spores which splash onto nearby plants, or move through standing water or saturated soil to infect new plants (read more about how Phytophthora blight spreads). You can significantly reduce the number of additional spores being produced in your field by removing and destroying (bag, bury or burn) infected plants.


Soil and plant health.
There are many factors which affect whether or not a plant becomes sick. Although benefits are not always easy to quantify, healthier soils are more likely to contain beneficial microorganisms which may compete with Phytophthora blight and result in less-severe disease. A holistic approach to improving soil health and quality will also improve drainage and is an important part of an integrated Phytophthora blight management strategy.


Chemical control
Chemical fungicides can be a valuable part of an integrated control strategy for Phytophthora blight. However, the water mold which causes Phytophthora blight (Phytophthora capsici) is a highly variable and changeable (or “plastic”) organism, and resistance to a particular fungicide can develop relatively quickly in a population. In New York, resistance to the fungicide mefenoxam (Ridomil) is already widespread in populations of P. capsici on Long Island and in the Capital District (see map), so this chemical should not be used in these regions. When possible, fungicides with different chemistries should be used in rotation to control Phytophthora blight, because this slows the development of resistance in a Phytophthora blight population. As always, fungicides must only be used according to their labels.



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