Knowledgebase

Early Potato Blight and 2026 Planning #926735

Asked March 25, 2026, 1:07 PM EDT

UVM Extension assisted us last summer in identifying, via some plant specimens, that we had a big case of early blight in our potato garden at the Deborah Rawson Library in Jericho. We are planning this year’s garden and have some questions about prevention. We are unable to do adequate crop rotation as the two areas in which we do rotate the potatoes and squash are only a few feet apart. Given that limitation: 1. Do you have a recommendation for a certified disease free potato that we could purchase to minimize the risk of developing early blight again? 2. The references from last year’s email were very helpful but the fungicides they recommended were not organic. Upon some research, I see that Serenade (a copper based fungicide) has some benefit but that potassium bicarbonate products, like Milstop, may be better. I’ve seen some reference to Storox (a hydrogen peroxide mix) that might also be helpful but more costly than the others. Do you have any opinion on these organic products ( I think they are all organic)? 3. My understanding is that any of the fungicides are not applied until the first evidence of disease, correct? 4. Would heavy mulching with straw or hay be helpful in preventing some of the spores in the soil from splashing up onto the plants/ 5. Would cutting off the lowest potato plant leaves, as one might do with tomatoes, be helpful in the potato crop? 6. In regards to our potato beetle problem which was more noticeably bad last year than ever before, do you recommend delaying planting to avoid the life cycle of the beetle and minimize beetle presence? We typically plant the potatoes in the middle of May but there is some thought to delaying that until the end of June to get past the beetle life cycle. Those who suggest that have not experienced a delay in harvesting which would be our preference since we try to harvest in mid September, using that harvest as a community and pre school project. October can be a bit colder and less conducive to harvesting with those groups.

Chittenden County Vermont

Expert Response

Hello Susan, Thank you for reaching out to the UVM Master Gardener Program again.

Here are some suggestions for dealing with early blight on your potatoes:

Crop rotation: I know that you said that this was not feasible given your space.

Using only clean seed (and preferably a seed with some level of resistance to early blight). While there is no immunity to early blight, these varieties carry some resistance to it: Russet Burbank, Lamoka, Snowden, Lehigh, Ranger Russet, and Elba.

Avoid irrigation in cool, cloudy weather and allow time for the plants to dry out before nightfall.

It's important to promote good air flow around your plants. .

Maintaining good weed management will help (especially weeds that are also susceptible to blight) so heavy mulching should assist with that.

Keeping the right balance of nutrients for your potatoes will help them cope with disease.

This is a great resource from the University of Maine:

https://extension.umaine.edu/ipm/ipddl/publications/5087e/

And a helpful blog:

https://blogs.cornell.edu/livegpath/gallery/potatoes/early-blight-on-potatoes/


As for the potato beetle, cultural practices can play a big part in reducing their impact. Practices such as crop rotation, trapping, mulching, row covers and flaming have been shown to be effective in minimizing the need for pesticides. For small gardens, dropping adults and larvae into soapy water and removing the eggs can be effective. Another cultural practice is to plant an early maturing variety (check seed catalogs for seeds that mature in less than 80 days). This will allow the potatoes to mature and be harvested before the mid summer onslaught of adult beetles.

Here are some good links:

https://www.uvm.edu/vtvegandberry/factsheets/potatobeetle.html

https://extension.umn.edu/yard-and-garden-insects/colorado-potato-beetle#cultural-controls-3562761

I consulted with our resident pesticide expert and this is her recommendation:

At the end of the season (earlier for early potatoes), I usually see a lot of damage from both early blight and potato leaf hopper (causes leaf edge dieback). I am not sure either really impacts yield much the way an infection of late blight would (caused by a different very aggressive fungus like pathogen). The most effective organic fungicide would be one that contains copper. There are several on the market with various names for organic gardeners. Here is an example https://bonide.com/product/liquid-copper-fungicide-rtu/. It would need to be applied at first sign of disease and repeated on a weekly basis (or whatever the label recommends) until harvest to protect new tissue and to protect foliage where the fungicide has weathered off. Hand picking leaves does not usually work because you don't see all the leaves where infections are just starting, but pruning off lower leaves would improve air circulation so you may see a delay in infection severity. THe mulch is a great idea to prevent rain splash up to the lower leaves and keeping up vigor of the plants is important because they will better withstand disease or insect attack. The use of hydrogen peroxide products works fine for killing the spores that are active right then, but it has no residual effect like copper so it is usually not that effective. I have noticed that earlier potatoes go down earlier from leafhopper and early blight whereas the later potatoes aren't as bothered until later. It may help to try some of the resistant cultivars above or select a longer season potato. Colorado potato beetles are tough and you can hand pick. They can be managed with organic insecticides but only when they are in the very small larval stage. Spinosad can be used organically for some control.


I hope that answered all your questions and I wish you good success in the garden this year!

Suzanne

Suzanne Garrity, UVM Extension Master Gardener Volunteer Replied March 26, 2026, 6:22 PM EDT

Loading ...