We tell gardeners, new and experienced, that herbs are easy to grow. They don’t require a lot of watering, maintenance, and are free of diseases and insect pests. Some herb plants even help to ward off these garden problems. Guess it is time to qualify that statement after giving it some thought because we have had some of these nuisances in our herb beds.
For the most part we don’t think too much about an aphid here or there on the lemon verbena or a slug hiding in the marjoram. At the end of the growing season many plants get powdery mildew and that’s just part of the cycle. But if there is a whole infestation of aphids, as there has been once or twice on the lemon verbena, then Super Gardener has to come to the rescue.
For the most part we don’t think too much about an aphid here or there on the lemon verbena or a slug hiding in the marjoram. At the end of the growing season many plants get powdery mildew and that’s just part of the cycle. But if there is a whole infestation of aphids, as there has been once or twice on the lemon verbena, then Super Gardener has to come to the rescue.
So, what are aphids? The Aphididae family has over 4400 species and about 250 are destructive to most common garden plants. They can be tiny black bugs or green or white, reddish, pinkish, or brown. Little vampires that they are, they suck the plant sap out of the plants’ leaves to the point that the plant could die. They are usually hiding on the underneath part of the leaves or along new growth of stems. Aphids come into this world as nymphs ready to quickly mature into adults, 7-10 days, then turn around and make 80 more of themselves. Suffice it to say this is the short version of their life but if you are interested in more about these critters look here. What most of us really want to know is how to get rid of them.
If there aren’t too many, rubbing them out with your fingers is easily done. If that’s too gruesome then shake them into a pan of soapy water (1 tsp dish soap, pinch of cayenne and a quart of water). Or put the soapy water in a spray bottle and spray it on the plant. Commercial insecticidal soaps are also available in garden centers. Once the aphids are gone, dusting the plant with flour or diatomaceous earth will help them stay away. Companion plants such as garlic, chives, catnip and yarrow also help to repel these little sap suckers. We have found yarrow to be especially beneficial by our roses. Frogs and ladybugs find aphids to be tasty and will help keep the population down, so encourage them to hang out near and on your plants.
If there aren’t too many, rubbing them out with your fingers is easily done. If that’s too gruesome then shake them into a pan of soapy water (1 tsp dish soap, pinch of cayenne and a quart of water). Or put the soapy water in a spray bottle and spray it on the plant. Commercial insecticidal soaps are also available in garden centers. Once the aphids are gone, dusting the plant with flour or diatomaceous earth will help them stay away. Companion plants such as garlic, chives, catnip and yarrow also help to repel these little sap suckers. We have found yarrow to be especially beneficial by our roses. Frogs and ladybugs find aphids to be tasty and will help keep the population down, so encourage them to hang out near and on your plants.
A couple of summers ago our basil was hit by downy mildew and we lost the entire crop within days before we were able to harvest much. Downy mildew spores appear in large numbers on the lower surfaces of leaves, so may hide from your view without close inspection. As the basil was harvested the underside of the leaves appeared “dirty” as if soil had splashed up on them. However, it didn’t wash off. In the presence of water from recent irrigation, rain or heavy fog, the spores will germinate within four hours. Spots appear and are covered with a layer of fungus that can be white to purplish to almost black. The entire leaf dies quickly.
Usually older leaves are affected first, then younger leaves. Petioles (the little stem that holds the leaf to the main plant stem) remain green even after the leaf dies. We found downy mildew a death sentence and didn’t see any way to stop it. It spreads very quickly from water splashing onto the plants. However, several garden sites have a few recommendations: prune effected areas and plants as soon as the mildew is found. A copper spray may be used as a preventative.
There are a few other preventative measures and we have put those into place since that deadly summer as all the different basils we grow are very important to our business. We use wider spacing between plants, whereas we used to simply scatter plant the tiny basil seeds we take more care to spread them out to promote good air circulation and leaf drying. We water early in the morning to allow leaves to dry thoroughly. There is one thing we do not do that is recommended, avoid overhead watering. In the big garden where the basils grow we have overhead sprinklers, so if you can water differently it would be a good idea.
It appears that downy mildew on basil has been problematic for quite some time. Rutgers University has been working several years on a resistant basil and has developed a variety that is resistant to downy mildew. Johnny’s Seeds now has Prospera and Rutgers Devotion and we have purchased both to add to our seed repertoire.
Usually older leaves are affected first, then younger leaves. Petioles (the little stem that holds the leaf to the main plant stem) remain green even after the leaf dies. We found downy mildew a death sentence and didn’t see any way to stop it. It spreads very quickly from water splashing onto the plants. However, several garden sites have a few recommendations: prune effected areas and plants as soon as the mildew is found. A copper spray may be used as a preventative.
There are a few other preventative measures and we have put those into place since that deadly summer as all the different basils we grow are very important to our business. We use wider spacing between plants, whereas we used to simply scatter plant the tiny basil seeds we take more care to spread them out to promote good air circulation and leaf drying. We water early in the morning to allow leaves to dry thoroughly. There is one thing we do not do that is recommended, avoid overhead watering. In the big garden where the basils grow we have overhead sprinklers, so if you can water differently it would be a good idea.
It appears that downy mildew on basil has been problematic for quite some time. Rutgers University has been working several years on a resistant basil and has developed a variety that is resistant to downy mildew. Johnny’s Seeds now has Prospera and Rutgers Devotion and we have purchased both to add to our seed repertoire.
Powdery mildew, not to be confused with downy mildew, can also occur on herb plants, as well as many vegetable plants. We have found it usually appears later in the summer when the weather is drier and warm, common conditions that promote this fungal growth. It shows up as dusty splotches of white or gray powder on the leaves and stems where we notice it on the surface of leaves, but it actually typically starts on the undersides of the leaves. It is a common nuisance but typically not fatal, although it certainly sucks nutrients and energy from plants and leaves can yellow and fall off the plant.
As with downy mildew, removal of infected plant parts is a place to start. Spraying with a copper based fungicide can also be beneficial. Because the mildew is “host specific” the fungus on the monarda won’t infect the catnip. But once it gets on a plant it typically returns each year since the spores live in the debris around plants. There are a few preventative measures that can help and as with downy mildew giving plants plenty of circulation is important, no overhead watering and avoid fertilizing if the mildew is present. If you know a plant is susceptible, try a preventative spray starting early in the season and continuing throughout the summer.
Perhaps our attitude towards powdery mildew is somewhat causal – because it happens late in the summer we often just ignore it. We find it on the comfrey, bee balm and almost into fall on the calendula. By the time it appears we have mostly completed the harvesting of these plants, so we see it as a natural progression of the herb garden, with plants telling us they are done for the season.
As with downy mildew, removal of infected plant parts is a place to start. Spraying with a copper based fungicide can also be beneficial. Because the mildew is “host specific” the fungus on the monarda won’t infect the catnip. But once it gets on a plant it typically returns each year since the spores live in the debris around plants. There are a few preventative measures that can help and as with downy mildew giving plants plenty of circulation is important, no overhead watering and avoid fertilizing if the mildew is present. If you know a plant is susceptible, try a preventative spray starting early in the season and continuing throughout the summer.
Perhaps our attitude towards powdery mildew is somewhat causal – because it happens late in the summer we often just ignore it. We find it on the comfrey, bee balm and almost into fall on the calendula. By the time it appears we have mostly completed the harvesting of these plants, so we see it as a natural progression of the herb garden, with plants telling us they are done for the season.
Another fungal disease that can be problematic is mint rust. This disease shows up as orange or rust colored spots on the underside of the leaves. We typically see it in late summer, again after we are through harvesting mints. We have moved into the basils and other perennials so we ignore the rust. As with other fungi start by removing infected plants. Be sure there is good circulation among the plants and avoid overhead watering.
A couple of recommendations for dealing with these fungal problems: grow some herbs in containers, water from the base of the plants, clean debris from around the container each year. Some gardeners would recommend completely digging up the infected bed and moving any uninfected plants to a new area. The old area could be treated with a fungicide and not used for several years. Another choice would be to cut down the herb that’s there and dispose of the infected plants but not in the compost. Burn them or put them in the garbage. Then try treating the bed with one of the newer biological fungicides that are bacteria based. These products are acceptable for organic gardening and edible crops where most fungicides are not. An example is Serenade found in most garden centers. It is OMRI approved and won’t harm bees or beneficial insects. Our kind of commercial spray if we have to use one. Next mix the product according to directions and drench the soil all around the growing area and just a bit beyond. Finally, begin spraying with the product according to directions regularly as the plants begin to grow. Only water in the morning, and only water once a week.
A couple of recommendations for dealing with these fungal problems: grow some herbs in containers, water from the base of the plants, clean debris from around the container each year. Some gardeners would recommend completely digging up the infected bed and moving any uninfected plants to a new area. The old area could be treated with a fungicide and not used for several years. Another choice would be to cut down the herb that’s there and dispose of the infected plants but not in the compost. Burn them or put them in the garbage. Then try treating the bed with one of the newer biological fungicides that are bacteria based. These products are acceptable for organic gardening and edible crops where most fungicides are not. An example is Serenade found in most garden centers. It is OMRI approved and won’t harm bees or beneficial insects. Our kind of commercial spray if we have to use one. Next mix the product according to directions and drench the soil all around the growing area and just a bit beyond. Finally, begin spraying with the product according to directions regularly as the plants begin to grow. Only water in the morning, and only water once a week.
Hopefully this helps qualify our statement about how easy herbs are to grow. Our problem is that we have chosen to minimize these insect and disease issues and what you chose to do now that you have more knowledge will be up to you. Knowing there’s a good organic spray, we may choose to change our habits and begin spraying some of our mints so we can prolong our harvests. We have already changed some of our behavior around basils and are more vigilant to watch for aphids early in the growing season on the lemon verbena. Always lots to learn when gardening and often “Ah-Ha” moments that help us improve what we do to grow better, healthier plants.
Resources:
https://purdue.edu
https://www.epicgardening.com/aphids/
https://www.thespruce.com/powdery-mildew-1402500
https://www.gardeningknowhow.com/edible/herbs/mint/treating-mint-rust-fungus.htm
Resources:
https://purdue.edu
https://www.epicgardening.com/aphids/
https://www.thespruce.com/powdery-mildew-1402500
https://www.gardeningknowhow.com/edible/herbs/mint/treating-mint-rust-fungus.htm