Yellow spots on zucchini leaves - Ask Extension
Hi, my zucchini and squash plants looked great until yesterday (7/20), when they suddenly developed these yellow spots. Mainly on one zucchini, but th...
Knowledgebase
Yellow spots on zucchini leaves #200930
Asked July 21, 2014, 9:11 AM EDT
Hi, my zucchini and squash plants looked great until yesterday (7/20), when they suddenly developed these yellow spots. Mainly on one zucchini, but the squash next to it had a few bad leaves also. There are also some yellow spots on my sugar snap peas, but not as bad. I removed the diseased leaves and sprayed with neem oil last night and this morning. I don't see any pests. Day before yesterday, I watered with fish emulsion, and it got pretty hot yesterday. I am in Highlands Ranch. They are in a raised bed in a sunny spot. Thanks in advance for your help!
Douglas County Colorado
Expert Response
First of all, thanks for sending this great photo. This does appear to be stippling caused by insect damge, but I can't be sure unless I can see an insect. Did you see any insects on the undersides of the affected leaves? I would suggest you keep checking the plants regularly to see if any more leaves become infected.
You should identify the souce of the condition before applying a treatment.
Regarding the use of Neem oil - This should not be used when temperatures are high and should only be used once a week. The oils can burn the leaves, especially in your sunny environment. If you do use it, apply it at night so the plants have a chance to absorb it.
Let us know if you continue to have issues with these plants. You can bring in the affected leaves for a more accurate diagnosis and treatment program.
You should identify the souce of the condition before applying a treatment.
Regarding the use of Neem oil - This should not be used when temperatures are high and should only be used once a week. The oils can burn the leaves, especially in your sunny environment. If you do use it, apply it at night so the plants have a chance to absorb it.
Let us know if you continue to have issues with these plants. You can bring in the affected leaves for a more accurate diagnosis and treatment program.
Thank you for your response. I did not see many bugs on the leaves. I found one of the green bug, one of the dark bug, and a few light-colored tiny bugs. I have included more pictures, including the underside of an affected leaf.
Also, here is a photo of the yellow spots on the sugar snap peas.
Out of the two insect photos you provided, the small green insect, which appears to be a thrip, would be most likely to produce the effects on the leaves you show. The brown bug is an wearwig. Earwig damage shows up as holes in the leaves.
However, we have looked at the photos you sent and cannot reach a a definative diagnosis. Because treatment is so closely tied to the species, I recommend that you put out sticky traps and bring them in for ID.
However, we have looked at the photos you sent and cannot reach a a definative diagnosis. Because treatment is so closely tied to the species, I recommend that you put out sticky traps and bring them in for ID.
Hi:
you can make sticky traps by spreading Tanglefoot, a horticultural glue, to yellow cards and stapling them to a tongue depressor and stick it into the ground next to the plant. Or you can go to a good nursery and buy them all ready-made. Once you catch something, you can bring the trap into our office (if you're in Douglas County) or into your county's extension office. You could also try to take a photo and send it to us, if the insect is clearly visible. If you're in Douglas County, we're at 410 Fairgrounds Rd, Castle Rock (Plum Creek Pkwy exit, go east).
you can make sticky traps by spreading Tanglefoot, a horticultural glue, to yellow cards and stapling them to a tongue depressor and stick it into the ground next to the plant. Or you can go to a good nursery and buy them all ready-made. Once you catch something, you can bring the trap into our office (if you're in Douglas County) or into your county's extension office. You could also try to take a photo and send it to us, if the insect is clearly visible. If you're in Douglas County, we're at 410 Fairgrounds Rd, Castle Rock (Plum Creek Pkwy exit, go east).
