What is wrong with my basil?

[jaymine]

I'm new to gardening, and have been searching and searching as to what might be wrong with my basil.

None of the mold, wilt, mite pictures I've seen seem to be the same. The stems of the plant are very healthy. I have begun to notice that just before it starts to brown as in the second picture, parts of the leaves look shiny, as if raw, maybe? Not all of the leaves have it, and some plants have seemed to hold off longer than others, but now most of the leaves are showing varying degrees of symptoms.

I have pretty good eyes, so if it's a bug thing, I don't believe they're present (at least all of the time). Damage seems to be occuring quickly, I'll inspect leaves, and a few hours later, the shiny parts have started to happen, or wilt around the outside. I'm at a complete loss.

[rainbowgardener]

What do the under sides of the leaves look like? Your pictures get blurry when enlarged. Does the damage seem to be in little dots?


https://blogs.extension.org/mastergarden ... mildew.png

that is underside of the leaf showing basil downy mildew. It is a disease of basil that is getting a lot more common and is unfortunately deadly.

The top sides of the leaves won't show the little dots, just yellowed sections bounded by leaf veins, since the d.m. pathogen can't grow past major veins.

You didn't say where you are. So far, I think this disease is mainly confined to the eastern part of the country, from MA down to FL.

[jaymine]

Thanks for your response!

The undersides show nothing different than what is reflected on the topside: wilted, brown areas (or 'shiny' parts, right before they start to brown). I don't have a good picture with me as I'm not at home, but I can provide one later if needed. There is certainly nothing like the picture you posted.

I live in Hawaii. The plants sit on my apartment balcony, where it is shady, with sun in the afternoon.

[imafan26]

Hawaii does have downy mildew, but it would look like what Rainbow showed you on the bottom and the top of the leaf would look yellow between the veins. I think you may have thrip damage, there is a lot of that too especially since they have a very wide host range. Thrips are hard to see without a lens they may be 1/16 inch or less. You can try the white paper trick. Hold a white piece of paper under the leaf and tap the leaf onto the paper. If you see paprika moving then it is probably them. The best way would be to use a microscope or loupe, you need a little patience, and some dexterity but if they are there you will see them. Thrips have predators and usually don't kill plants, but will cause scarring of the leaves. They are not easy to control and herbs in general are limited in what can be used on them.

https://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7429.html

[jaymine]

Thanks, Imafan. I was able to get a powerful magnifying glass to take a look at leaves I'd pulled earlier; I would definitely believe bug damage, as it looks like those shiny/dying parts are a top layer missing. I haven't seen the culprits, yet. It only makes me feel slightly better that it's not rot or wilt or something that would need me to abandon them completely. I'll check out that link and see if there's anything to be done. Mahalo.

[imafan26]

I have a jeweler's loupe. It has different magnifications and it fits in your pocket. A gardening friend gave it to me for Christmas. It takes getting used to since you have to take your time to go over the leaf and keep everything in focus, but most of the time I can tell what it is by looking at the damage even if I don't always see the bug. Thrips and mites have similar damage, and I sometimes get them mixed up. Mites usually show up in warmer weather, but it doesn't really matter since the treatment is about the same.
https://www.amazon.com/Pocket-Microscope-Magnifier-Jeweler-Loupe/dp/B00ATMRDHM

https://www.fcsurplus.ca/shopping/produc ... th-Stands/

https://www.amazon.com/Illuminated-Jewelers-Loupe-40x-25mm-Lighting/dp/B007GJJRZC/

[jaymine]

I was able to borrow a loupe. The damage on the leaves hasn't gotten much worse during the last few days. The young leaves have signs of death on the outsides, but there hasn't been further damage like the yellow/brown spotting displayed in the picture on any of the bigger leaves.

I haven't been able to spot anything either (and yes, getting the tiny leaves into focus is a challenge!). What do you use to treat? Plant oils?

[imafan26]

As long as it does not get over 80 degrees horticultural oils will work. However, in Hawaii, that is for a limited time, unless the plant is in a pot and you can dunk it and keep it in the shade for a day so it does not get burned.

I actually use 70% alcohol. Again do not use it in the heat of the day. Spray in the early morning is best or in the evening when the leaves have a chance to cool down. It acts as a dessicant and works for most things. Sometimes I just use water and hose of the bottom of the leaves every day to dislodge what might be under them. That can be tricky though since basil leaves bruise easily.

[jaymine]

Well, that is easy and readily available! I will certainly give that a try. I'm assuming I should try to keep the spray out of the dirt...

[imafan26]

Yeah, some of the spray will probably drift but you don't pour the bottle on it, so it is usually o.k. Get the 70% alchohol. 90% costs more but is not any more effective. Use the sprayer from any bottle of cleaner, make sure it is thoroughly cleaned out first, and residual cleaner will cause necrotic spots. The sprayer top will fit on top of the alcohol bottle. I usually recap the alcohol after I use it with the original cap because alcohol evaporates.

You don't say where you live but you can bring your leaf to the Master gardener office M-F , 8a.m.-12 p.m at the Pearl City Urban Garden Center. There is also a booth on Second Saturdays at the Garden 9-11 a.m. at Urban Garden. Have the master gardeners look at the leaf under the microscope. You can also go to one of the other plant doctor booths. If they cannot identify the problem they can take the sample back to the office. Bring it in a sealed bag please.
https://www.ctahr.hawaii.edu/uhmg/Oahu/#out

[jaymine]

Thanks again for the help and info! I really do appreciate it.

Unfortunately, I live on Maui, but I'm going to look up now to see if there is something similar here. (I had no idea.)

[imafan26]

Maui also has master gardeners below is a link to their office hours. They work out of the UH extension office. They do not have a public garden to visit and I don't know what kind of outreach they have, but they are a dedicated bunch. I met a few of them when they came to the master gardener conference.

There are master gardeners on Oahu, Maui, Kauai, an two are on the Big Island to help the home gardeners.

https://www.ctahr.hawaii.edu/UHMG/Maui/index.asp