Category Archives: Plant Problems & Diseases
Squash plants love the hot summer sun, and Kansas has plenty of it! Any vegetable gardener in the state who has been growing for very long will likely have planted some variety of squash. There are a few issues that can pop up when growing squash, but overall, it is usually pretty easy to grow.
In the Demo garden, we are growing both summer squash and winter squash. Contrary to what the names imply, both types of squash are grown during the heat of summer; one main difference is that summer squash is grown for its young or immature fruit (think zucchini), while winter squash is grown for its fully mature fruit, so it takes longer to be ready (think butternut squash or pumpkins).
Summer squash grows in a bushy shape and is generally ready to harvest by mid-summer. When harvested at small sizes, they have a soft, thin skin and unsubstantial seeds and can be eaten raw. If left on the plant to grow very large, though, they become tough and too bitter to eat raw. The most popular types of summer squash are zucchini and yellow squash, but other types include pattypan and tromboncino.
We have two varieties of summer squash in the demo garden, and both are varieties of zucchini: ‘49er’ and ‘Astia,’ which both are beginning to yield a harvest.
‘49er’ is a yellow zucchini which has about 50 days to maturity (DTM), and ‘Astia’ is a dark green zucchini with 48 DTM. Both are best harvested at about 5-6 inches long. (Yellow squash and yellow varieties of zucchini are similar, but different; zucchini maintains a relatively consistent diameter, whereas yellow squash is broader at one end and tapers toward the other, and often has a slightly thicker skin than zucchini.)
Winter squash generally has a vining nature and needs either lots of space to sprawl out or a trellis to grow vertically when space is at a premium. Because it is harvested when fully mature, it has a tougher skin than summer squash that is not usually eaten. Winter squash is usually ready to harvest late summer or early fall. One of the benefits of growing winter squash is that it can store well, even through the winter months. The winter squash in the demo garden (‘Waltham’ butternut and ‘Autumn Frost’ acorn squash varieties) are setting fruit but won’t be ready to harvest for several more weeks. We’ll keep you posted!
A couple of the biggest challenges with growing squash are the squash vine borer and the squash bug. Both of these insects can wreak significant havoc and are taking their toll now in the Demo garden.
The classic symptom of squash vine borer is a wilted plant when the plant has been watered well and shouldn’t be drooping. Upon closer inspection, you may be able to see that the stem has small holes or is chewed up close to the ground with larvae frass at the base. At this point, it is important to remove the larvae by either disposing of the plant completely, or, if you’re feeling surgical, slitting the vine with a sharp knife until you find the larvae and then removing it. The slit vine can be placed back in the soil and kept moist in the hopes that it will send off new roots, but some plants may have been damaged beyond repair and won’t recover from the “surgery.” If the larvae are not removed and are allowed to complete their life cycles in your garden (in which they eat their way out of the stem, burrow 1-2 inches into the soil, and wait in a cocoon until the next season), the problem will likely return next year. Once you have squash vine borers, there is not a whole lot you can do; to learn about treatment options and cultural controls, see this helpful publication.
Another pest we are facing in the Demo garden is squash bugs. Adults look similar to stink bugs and can be found on many species of the cucurbit family, but squash is their favorite. Adults and nymphs (which are lighter grey with black legs) cause damage by sucking out juices from plant leaves, resulting in yellowing, wilting, and death of the plant when populations are large. Squash bug eggs can be found by scouting on the under sides of leaves – they are glossy brown and laid in groups in between leaf veins. These eggs can be scraped off and disposed of to help control, but here in the Demo garden, the problem has passed the egg stage, and we have begun chemical control to limit the damage. Squash bugs are best controlled at the nymph stage, since adults have a hard shell that protects them from pesticides. We have applied one round of spinosad by spraying it on the vine and branches where the nymphs are congregating. We won’t be able to harvest zucchini for at least three days after spraying, and depending on what the squash bug population looks like after the application, we may spray again in about a week. We use chemicals sparingly in the Demo garden, which are safe when used appropriately. As always… when using chemical pesticides, make sure read and follow the label! To learn more about squash bugs, click here.
One last issue we had with the zucchini earlier this year was small fruit (around 3 inches) that shriveled up or rotted from the blossom end of the fruit before coming to harvestable size. This symptom can be due to a couple of different culprits, but is ultimately related to an issue with pollination.
Sometimes high temperatures following a mild or cool spell can limit the number of pollinators that are active in the garden; sometimes over-fertilization (high nitrogen levels) in the soil can cause the plant to produce too many male flowers; and sometimes plants don’t produce enough male and female flowers at the same time to ensure enough pollination (this issue usually resolves itself as the season progresses.)
We stepped in to lend our zucchini plants a pollinating hand, and you can too if you see this issue in your garden – it is as simple as taking the pollen from the male flowers and transferring it to the female flowers. First, identify which flowers are female and which are male; female flowers often have a swelling behind the flower head where the fruit is barely beginning to form, whereas male flowers have a straight stem behind the flower head. Another, perhaps more reliable way to tell is to look inside the flower: the female has a stigma which is larger and slightly round or bulbous, and the male has a single, straight appendage – the anther – inside the flower.
Hand-pollinating can easily be done by using a small artist-sized paint brush to transfer pollen from the male to the female flowers; lightly touch the tip of the brush to the anther on a male flower and dab the pollen that the brush picked up onto the stigma of a female flower.
With a couple hand-pollinating sessions, a relative evening-out of temperature, and an uptick in pollinators in the garden, our zucchini are now producing harvestable fruit. Now it’s a matter of fending off the squash bugs so that we can keep harvesting this delicious summer garden staple!
Resources for further reading:
By: Maureen Wilbeck, Master Gardener
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.
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.
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.
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!
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.
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!
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.
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.
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.