Category Archives: Plant Problems & Diseases

Watch for Diseases in Your Garden

As nice as the rain and hot-but-not-scorching weather is, it is creating something of a perfect storm for tomato diseases this summer. Our two most common tomato diseases are Septoria Leaf Spot and Early Blight. While they are two different diseases, we usually talk about them as one disease because they develop in the same conditions and have the same overall effects on the tomato plants.

This is a tomato leaf that is infected with Early Blight. The lesions usually have concentric circles, and spread to have something of a V-shape on the edge of a leaf. In contrast, Septoria Leaf Spot has small round spots over the whole leaf. Some years we see more of one or the other. Some years we have both. The disease typically starts on the lower leaves of the plant and works up the plant. Most of the time, we don’t really start noticing a problem until the first infected leaves start to turn yellow and die.

The disease spreads from splashing water, which is why it is usually worse when we get rain. It also requires humidity and warm nights, which we have had in spades the past week! We have also had lots of dew, which is great for disease development.

As with most garden problems, the best thing to do is to try to prevent the disease from starting. There are a number of cultural practices that can help prevent these diseases or reduce their spread.

1. Mulch under plants to prevent water splashing from the soil onto lower leaves. (The disease overwinters on plant debris, often in the soil. No, there isn’t any soil treatment.)

2. Use cages, staking, or some method to help your plants grow upright rather than sprawling on the ground.

3. Space your tomato plants 2-3 feet apart to promote airflow.

4. Water the soil and avoid getting water on the leaves if at all possible when watering.

5. Prune out suckers below the first flower cluster (especially on indeterminate tomatoes) to promote airflow.

6. Scout regularly for signs of disease and remove infected leaves right away.

7. Rotate where you plant your tomatoes as much as possible.

8. Remove infected plants from your garden every year at the end of the season and do not compost them.

Sometimes, even if we do everything “right” we still end up with these diseases, especially when the weather conditions are ideal for disease to develop.

The good news is that these diseases usually do not kill the plants, and they will not spread as quickly if it turns hot and dry. The worst damage (other than a weaker plant that is more susceptible to spider mites) is that if there is too much defoliation, then there is a much higher risk of sunscald on the fruit.

Using Fungicides

If you want to try to prevent development of these diseases, now is the time to start spraying a fungicide. You will probably need to spray once a week as long as we are experiencing this type of weather pattern.

If you are looking for organic options, you can use a copper-containing fungicide, such as a Copper Soap. There is also a biological fungicide that contains Bacillus subtilis, usually sold under the name Serenade. The key with the organic options is to use them regularly, especially before you have lots of disease, because they will work better if the disease pressure is low.

Conventional fungicides that are commonly used are chlorothalonil and maneb, which are found in several different garden products. They are a little bit stronger, but will still be most effective if they are used preventatively.

Fungicides are not usually curative, they just prevent the further spread of the disease. None of them are perfect either – the weather and how you apply them affect the efficacy of the treatment.

On that happy note, I hope your gardens all got a good drink this morning! We had about 1.5″ in the rain gauge, so no watering for us for a few days.

Not a Fan of Crazy Weather

That would be the spinach that isn’t a fan of the crazy weather!

This is the ‘Bloomsdale’ spinach that was supposed to be more bolt tolerant…or not. To be fair though, when the temperatures bounce around like they have been this spring, it does tend to initiate blooming/bolting in leafy greens more often than not. When we harvested last week, I saw that some of the leaves were starting to get more pointy, which is often an early sign of bolting. This week there were a couple of the plants in full flower, like shown here.

The ‘Sagar’ Spinach in the Taste of India garden wasn’t quite as far gone, but you can see here the initiation of the flower bud.

We harvested the good leaves off of both patches of spinach this week and then removed the plants. We also harvested the rest of the romaine lettuce and a good bunch of the mustard greens!

A Bug & Pest Round Up

All of a sudden last week the population of bugs, pests, and other problems seemed to explode in the Demo Garden!

All of a sudden near the end of last week the spider mites came on strong. This poor specimen is on the ‘Iron Lady’ tomato. It may be resistant to blight, but it is clearly NOT resistant to spider mites. There are several plants with varying numbers of spider mites on them, but this is one of the worst. The typical “first” line of defense is to spray with a hard stream of water. Given the humidity, the next option is neem oil, horticultural oil, or insecticidal soap. These products need to be sprayed every 5 days or so when it is hot, until new damage isn’t occurring. Unfortunately, is you spray when it is hot out, they can actually damage the plants, so you need to spray in early morning.

In the realm of four-legged, furry varmints, it appears that we have some critter that is enjoying the almost-ripe tomatoes. My guess would be a squirrel, because of the bite marks and also because we’ve had that problem before. The ants are just opportunists here!

I’ve also seen stinkbugs around the garden, which is an insect we don’t normally see a lot. Here’s a stinkbug on one of the cherry tomatoes.

Here’s another look at a stinkbug, this time on one of the eggplants. Stinkbugs are “true bugs,” and they feed on plants and fruit by puncturing and then sucking out the juices. On tomato fruit you will often find yellow or white spots just under the skin where they have been feeding. They don’t damage the edibility, just the prettiness. They can be pretty destructive though given a high enough population. They can also feed on the plants themselves and can have similar effects to aphids and spider mites. How to get rid of them? Well…it depends what you are willing to do. The reality is that it is pretty difficult to kill those hard-backed bugs. Since we aren’t seeing very many of them, we aren’t going to do much at the moment, which we will probably regret in a few weeks.

Here’s what the stinkbug damage looks like on a tomato. The tomato is still perfectly edible, it just looks kind of ugly.

The Arkansas Traveler tomatoes all of a sudden are showing these “crop circles” on the fruit. To me, this looks like Tomato Spotted Wilt Virus. The plant doesn’t look particularly bad, although I commented earlier on the fruit being smaller than advertised. A virus would partially explain that. There is perhaps a little bit of necrosis (dead areas on leaves) at the shoot tips. The question is how it got the virus. This virus is typically transmitted by thrips in a greenhouse. Well, this plant was raised in my office, and I don’t think there were any thrips or infected plants for the thrips to pick up the virus. My guess would be that it was infected with the virus outside, either by thrips that picked up the virus last year and overwintered or infected thrips that were on one of the plants that did come from a greenhouse. At any rate, there’s nothing we can do about it now.

This is a pepper with a bad case of sunscald. Typically tomatoes and peppers are the most susceptible to sunscald, especially when there is lots of hot, bright sun. Keeping plants healthy with lots of leaf cover is the best option. Some varieties are better than others as far as shading fruit. At other times if you are having a very severe problem, providing a little additional shade would be the only option, which can sometimes be a logistical challenge in a garden!

Our sunflowers in the Kids Snack Garden are getting rather holey and spotted leaves. On examination, I found these little lacebug nymphs on a couple leaves.

And also these little white caterpillars. I think they are just a type of wooly bear caterpillar, even though they are white. If anyone knows differently, please let me know! These guys are having quite a meal of sunflower leaves. At this point, I’m not going to do anything about the bugs on the sunflowers. Now if they encroach onto a vegetable…

Some of the eggplant leaves are also looking a little bit Swiss Cheesy. I couldn’t find anything on the plants, although my suspicion is cucumber beetles. I found a couple flea beetles, but they typically cause pinhole size damage. I’ll be keeping an eye on the eggplant to monitor the damage and to see if I find anything doing the chomping. When you see the pile of eggplant we harvested today, you won’t be to concerned about our plants!

If you remember from a couple weeks ago, I showed some pictures of the Chocolate Cherry tomato and was suspicious of either a fungus or bacterial canker on the plant. Well…I sent a sample to our plant pathology lab, and they said that it was scorch. I’m not convinced, because there were lesions on the stems. They could have been from one of the hail storms. At any rate, the plant is not recovering and seems to still be in decline. We removed it today. The neighboring roma seems to be developing some sort of ailment, but it might just be a combination of spider mites, early blight, and a slight nutrient deficiency.

After all that death and destruction, here’s a palate cleanser! Yes, this Swallowtail Butterfly Caterpillar is munching down the fennel, but we planted it for that purpose anyway!

Tomato Update

Our tomatoes are generally looking great this year! After 2 years of tomato heartache and heartbreak (heat one year, herbicide injury and heat the next), we finally have some great looking tomatoes again. We’re starting to see a touch of Early Blight here and there, and there’s also a little bit of residual herbicide damage that is just now showing up. Most of the plants have fruit set and are growing like weeds! We haven’t fertilized at all, other than a little bit of a liquid starter fertilizer at planting and working in some compost this spring.

The ‘Taxi’ tomato plant (orange fruit) is the early leader as far as fruit set. I’m withholding judgement until they ripen without excessive cracking, however.

I’ll be honest that I’m excited about this funky tomato. This is one of two fruit that I’ve seen set on the ‘Limmony’ plant. It is an heirloom that can get up to 1 pound in weight! There will probably only be a few fruit from this plant anyway.

This is the ‘Arkansas Traveler’ tomato, and I’m a little confused so far by the shape of the green tomatoes. It is supposed to be a pink, round tomato at maturity, but the fruit are giving the impression of being a little more oblong. The number of fruit set so far is great for an heirloom.

This is our Chocolate Cherry plant in the Pizza Garden. It has some suspicious looking brown lesions on the stems and some brown, wilting leaves. I rather suspect it looks like Bacterial Canker, which is largely a seedborne disease. I knew I should have kept using the old batch of seeds, rather than buying new ones. A boiling water treatment before planting would also have helped. I’m still waiting for a confirmation on the diagnosis, but there’s a high probability that this plant is going to be removed. Sadness!

That’s just a quick overview of a few of our tomatoes this year. I’ll keep you posted on the poor Chocolate Cherry plant.

Troubles in Vine-Land

As I mentioned in passing on Tuesday, we have several different things going on with our vining vegetables – cucumbers, squash, etc. Actually, the melon plants are all still in good shape, so the problems are restricted to the cucumbers and various squashes.

Here’s the first one:

The cucumbers in the Family of 4 Garden are coated with these…any ideas? I’ve seen numerous samples of vine plants come in this month with the same signs and symptoms. I think what tricks folks is all of the white flecks. This is actually a severe aphid infestation. If you look closely, especially in the upper left corner of the picture, you can see the green buggers. In the middle of this picture is an ant…and ants like to “farm” aphids and protect them from predators so the ants can feed on the sticky honeydew that the aphids excrete as they feed. The white flecks? Those are the aphid “skins” as they grow and mature they “molt” and leave those white skins behind. I’m sure there’s a technical term, but I can’t remember off the top of my head.

To make matters worse, the cucumbers also have these terrible looking insects on them! Can it get any worse? Well, actually, you might recognize the one as a ladybug, and the black and orange lizard-like bug…that’s the larvae of the ladybug! These are the good guys that are enjoying quite a feast of aphids!

So, what are we doing about the aphids on the cucumbers? Well, honestly, the answer is nothing. We’ve gotten quite a bounty of cucumbers, and the plants are still doing pretty well overall. The ladybugs aren’t controlling the aphids at this point, although given a couple of weeks they might get there. Spraying would kill the ladybugs and may not do much to prolong the life of the cucumber vines. We’ll probably let them go and pull the plants out in a few weeks if they become completely unproductive.

On to the next problem… An observant Master Gardeners saw this on the underside of one of the squash leaves on Tuesday. Theses are squash bug eggs. I’ve gotten several questions about why we aren’t having problems with squash bugs in the garden this year. The answer has pretty much been that we’ve been lucky. The renovated garden may have helped that situation too. At this point, we aren’t going to bother spraying, since most of the squash will be leaving the garden soon due to the third problem we’re seeing…

Ugh…powdery mildew. This is a disease that we often see on zinnias and other common garden plants about this time of year. Usually you start out seeing round, powdery white spots on the leaves. It seems like most of our squash went from 0 to 60 in almost no time flat, because the leaves are pretty well coated on several different varieties of squash. There are treatment options, but they are most effective as preventatives or very early in the infection period. These plants just aren’t worth saving at this point. Besides, we’re tired of zucchini! There are powdery mildew resistant varieties, but they can still get the disease in a bad year.

As you can see, a lot of things are starting to go downhill fast in the garden this year. Luckily we’ve got some seeds started inside and garlic on order for later this fall!