Are my bean plants sick, or just stressed out?

July 2, 2021 11:33 AM

I am growing green beans and they have just started to produce pods. I have noticed some dead patches on a few of the leaves (pictures) and I am worried it is a disease of some sort. Is it? And how should I treat it if so?

Some more details:

• They are in a raised bed in partial shade. I water them if I notice the top inch or two of soil are dry, which is about once a week if it hasn't rained.
• This week it hit 97 degrees here in NYC. The leaves curled and wilted during the day but recovered at night. This is about when I noticed the brown spots. Maybe this is just moisture stress?
• I've looked up images of common blight and halo blight and the leaf spots don't have the yellow margins that I see in photos of those diseases. The pods themselves are still immature but look healthy, and the flowers are fine. The plants are still putting out new buds and setting fruit.
• I didn't inoculate my beans (I know! Next time!) but I amended with some compost when seeding so they should have enough N for now.

I don't want to be overprotective but if it is a disease I know the treatments get more drastic and less effective the longer you wait!

Thanks all!

posted by goingonit to Home & Garden (5 answers total)

Best answer: This looks like it could be sunscald. It seems very localized - the spots almost look like water drops refracted sunlight and burned the leaves - and the rest of the leaves look healthy. If this were my bean plant I wouldn't give it much thought - maybe take care to water the dirt rather than the leaves, but overall not too concerning. Beans are pretty hardy once established under good conditions and can take a beating without really affecting productivity.
posted by Knicke at 11:51 AM on July 2, 2021

Okay, before I even saw your post, I thought "heat stress." I've been dealing with stuff like this with plants all spring out here in Portland, Oregon (you know us from recent record-breaking temperatures - it was brutal!).

With a heat wave like that, extra watering is totally reasonable. I would not let container/raised plant beds go that long without water during excessive heat, especially with young plants. I have some plants in very large containers and water them every day during the heat if it's not raining, and every other day in normal summer temperatures if it's not raining.

So, I'd give your raised bed a good thorough soaking as soon as possible, and make sure to water under the plant (which is to say, water the soil, not the leaves). Early morning or later evening is better, but do it as soon as you can.

If you have some extra high temperatures in the forecast, I'd go ahead and water in advance, to get your plants strong. Stronger, healthier plants do a better job of fighting off pests and other problems.
posted by bluedaisy at 1:46 PM on July 2, 2021

Response by poster: Thanks both! I think that you're exactly right. I watered one morning during the heat wave and probably there was some residual water left on the leaves when the sun hit them which would explain everything. Luckily the danger is now past and we have had rain for the last three days running. It's annoying to water without hitting the leaves because of where the bed lives but I'll do my best!
posted by goingonit at 1:58 PM on July 2, 2021

You could try watering in the evening or at night? That would give several hours without sun for the plant to dry. Or, shake the plant/leaves a bit after watering to try to get some of the excess water off of the leaves.
posted by bluedaisy at 2:30 PM on July 2, 2021

Response by poster: I don't like watering in the evening because it attracts slugs! We don't get up to 97 THAT many times a summer, even in 2021, and we do get summer rain unlike in Portland, so I probably won't be in this position again this season.
posted by goingonit at 3:00 PM on July 2, 2021