something eating the basil? - Ask Extension
I am growing basil in pots on a deck. I sowed two varieties of downy mildew resistant (one was prospero) varieties which did very well last year. Grow...
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something eating the basil? #802008
Asked July 19, 2022, 1:07 PM EDT
I am growing basil in pots on a deck. I sowed two varieties of downy mildew resistant (one was prospero) varieties which did very well last year. Growth seems to have slowed down considerably recently and the leaves show evidence that something is eating them, though I cannot see anything. Three pictures are attached which show a number of leaves that have holes or ragged edges, etc. I would expect these plants to much taller and bushier, based on past years. The two pots with basil are on a dolly that I pull around several times a day to expose the plants to as much sun as possible. On the best days with optimal moving they will get close to 7 hours of sun with 2 or 3 moves at the right times (from approximately 8am to 3 pm, plus sometimes there is a bit of late-day sun as the sun goes in and out behind some trees (around 6m)--starting to vary more now that the sun is declining).
The other pot has much shorter and less leggy plants--they were sown later and so are younger, and look ok so far (no pix here). Seeds got mixed up so I don't know which plants are which variety. Thanks, Mark
Montgomery County Maryland
Expert Response
Hello Mark,
Chewed foliage can be hard to diagnose without the culprit present, and many leaf-chewing insects or slugs/snails don't hang around between meals to be detected. With basil, a prime suspect is a mollusk (slug/snail), and you can check under the pots or nearby sheltered, damp hiding spots for them waiting-out the day. Sometimes beetles, katydids, crickets, grasshoppers, or a caterpillar (that has since been eaten by a bird) chew some foliage before moving on or disappearing. You can inspect the foliage at night with a flashlight to see if you spot anything, including on the leaf undersides. If nothing is found, applying a treatment is not practical because we won't know which pesticide ingredients would be the most effective. (Plus, not many are approved for use on edible plants.)
Our two pages about slugs/snails may be useful; there's some overlap in content, but they are slightly different, which is why we're sharing both: Leaf damage can also be caused by weather, so if your area happened to get a bit of hail from recent storms or strong winds that whipped foliage around, that can tear leaves or damage unfurling leaves, which will cause them to expand unevenly and develop kinks, curls, or holes. Some of the leaf defects in the photos do look due to abiotic factors (the environmental causes that are not pest- or disease-related).
The plants appear to be otherwise healthy and not stressed, so slowing growth could simply be due to the plants getting ready to bloom. Basil has little tolerance for soggy or poorly-drained soil, and the resulting root decline can slow growth, but usually that also generates obvious symptoms like foliage yellowing and wilt, which is not evident here. If this is older potting soil (used for several years), it can both retain moisture for longer periods, stressing roots, and will be low in some key plant nutrients unless you've been fertilizing. Nitrogen [N] is one of the most important nutrients for supporting plant growth, particularly foliage, so a fertilizer heavier in N content compared to other elements would benefit the basil most when it needs supplementation.
If you find a suspect for the leaf damage and would like it identified, feel free to send us photos. We do see what looks like a solo stink bug nymph in one picture, but these do not chew leaves and the plant is not showing signs of significant stink bug feeding.
Miri
Chewed foliage can be hard to diagnose without the culprit present, and many leaf-chewing insects or slugs/snails don't hang around between meals to be detected. With basil, a prime suspect is a mollusk (slug/snail), and you can check under the pots or nearby sheltered, damp hiding spots for them waiting-out the day. Sometimes beetles, katydids, crickets, grasshoppers, or a caterpillar (that has since been eaten by a bird) chew some foliage before moving on or disappearing. You can inspect the foliage at night with a flashlight to see if you spot anything, including on the leaf undersides. If nothing is found, applying a treatment is not practical because we won't know which pesticide ingredients would be the most effective. (Plus, not many are approved for use on edible plants.)
Our two pages about slugs/snails may be useful; there's some overlap in content, but they are slightly different, which is why we're sharing both: Leaf damage can also be caused by weather, so if your area happened to get a bit of hail from recent storms or strong winds that whipped foliage around, that can tear leaves or damage unfurling leaves, which will cause them to expand unevenly and develop kinks, curls, or holes. Some of the leaf defects in the photos do look due to abiotic factors (the environmental causes that are not pest- or disease-related).
The plants appear to be otherwise healthy and not stressed, so slowing growth could simply be due to the plants getting ready to bloom. Basil has little tolerance for soggy or poorly-drained soil, and the resulting root decline can slow growth, but usually that also generates obvious symptoms like foliage yellowing and wilt, which is not evident here. If this is older potting soil (used for several years), it can both retain moisture for longer periods, stressing roots, and will be low in some key plant nutrients unless you've been fertilizing. Nitrogen [N] is one of the most important nutrients for supporting plant growth, particularly foliage, so a fertilizer heavier in N content compared to other elements would benefit the basil most when it needs supplementation.
If you find a suspect for the leaf damage and would like it identified, feel free to send us photos. We do see what looks like a solo stink bug nymph in one picture, but these do not chew leaves and the plant is not showing signs of significant stink bug feeding.
Miri
