What's Eating My Dahlias- Part 2

Dahlias are gorgeous! Unfortunately all the bugs think so too. Let’s talk about how to deal with some of the most common pests: grasshoppers, thrips, tarnished plant bug (TPB), cucumber beetles, and leafhoppers. These methods work well for the home gardener and small scale grower. I use organic pest control methods. There are plenty of other options out there but I choose organic on our farm so that’s what you’ll find covered here.

Let’s start with the most full proof pest control method: Prevent the pest from even touching your dahlia. This is accomplished by the use of organza bags— you know the kind they use for wedding favors.

These work extremely well for a cut flower operation or cut flower specific garden. They block everything from getting your blooms. However if you are enjoying your dahlias in a backyard garden style setting, you may not want to look at “dahlia lollipops” all the time. Kinda’ diminishes the joy of it.

Grasshoppers are the hardest to control in my opinion. There aren’t many organic sprays that will touch a hard bodied insect. The best control for a grasshopper that I’ve found is attracting birds to your garden. Birds love to eat grasshoppers. Adding a water source, even a small one, is a great way to attract birds.

If you have chickens, even better- they will devour them. Just make sure your plants are big enough to take a little chicken abuse. Usually grasshoppers don’t become a menace until the plants are blooming so at that point, allowing chickens into your dahlia patch can work. I used to use this method a lot until a fox got all our chickens.

Botanigarde Maxx is the only spray I’ve ever encountered that will kill a grasshopper and even it’s hit or miss— Grasshoppers move quickly so it’s hard to get the spray on them. If grasshoppers are a serious issue for you, consideration of the organza bag will have to be done. It’s the most effective method for grasshopper control.

Thrips are an annoying nemesis when it comes to dahlias. Timing is one of the best methods I’ve found for dealing with them. In my climate, thrips are a bad issue from mid- May to mid summer. Then they die back and aren’t found in high infestation level numbers. Thrips are probably the number one reason I don’t grow early season dahlias. Organza bags are reasonably effective against them but thrips are so small that they can get inside the bags sometimes. Various sprays will work on them and keep the populations under control but having perfect light colored dahlias is a challenge during thrip season. If you need dahlias during thrip season, stick with brighter colors- thrips are more attracted to whites/light colors.

A pyrethrin spray or a spinosad spray is a pretty effective tool against thrips. I highly recommend alternating what you spray. Also one round of spraying won’t cut it, it’s something you have to do regularly during the pest’s season.

Tarnished Plant Bugs and Leafhoppers - these 2 can be controlled by the same method. The yellow sticky trap is my best friend. Now— don’t freak out. I know, I know- small animals (birds, lizards, etc) can get caught on these and die. However, I’ve learned you can still use them but you gotta get crafty in how you hang them.

A yellow sticky trap is a card coated with a sticky substance that attracts particular pests. It’s great at catching small flying insects. You want to keep the card size to no larger than 3x5. I punch a hole in mine and hang them below my netting so that they are in the main plant canopy. Keeping it down in the plant canopy is key so that it’s less likely to be in a bird’s flight path. Also, I’ve learned you want to make sure the card can swing. This keeps lizards off of them. If you fasten it tightly so it’s immobile, baby lizards will crawl on it and not be able to get off.

Leafhoppers are important to control and they are often overlooked because they don’t show physical damage to your plant quickly. They do chew on the plant but it’s not super noticeable. However, they are vector insects- meaning they can take a virus from one plant to another. And in this day and age, when dahlia viruses are becoming more common, controlling leafhoppers will help protect your dahlia plant stock.

Cucumber beetles- other than grasshoppers, these are probably the most destructive of dahlia pests. They can chew a bloom incredibly fast. If you begin to see them in your field/garden, you want to act quickly because this is a pest you don’t want getting out of hand.

Once again, organza bags are the most effective method. But a spinosad or pyrethrin spray will work too.

One of the best things I did several years ago was to stop growing plants in the amaranth and squash plant families near my dahlias. Amaranth is a magnet for cucumber beetles. So much so that I’ve completely cut it from my crop list. If you can’t do that, move it as far from your dahlias as possible. I do still grow small quantities of squash and cucumbers in my veggie garden, but I have it as far from the flower field as I can go (and still be on my property).

So to sum it up- if you want a flawless dahlia, put an organza bag on it before the bud begins to open (in the green stage as shown in the picture above). If that option doesn’t appeal to you, then sprays and strategic plant placement are your best options. Also employ the sticky trap. Not only does the trap catch a lot of pests, but it’s pretty non-harming to you and others.

Is Something Eating Your Dahlias? Let's figure out what it is!

It’s that time of year. You’ve been watching with great anticipation as your dahlia bud begins to show color. It opens so slowly— or so it feels because it’s the first one and you’ve been waiting months to see a dahlia again (or maybe for the first time! Eeek!!) Then one morning you walk out and you see a hole in your leaf or the corner has been chewed!

How Dare They?? How dare some little creature enjoy breakfast from your dahlia petal!

Image by Valerie Miros- Grasshopper Damage

Don’t worry— there’s hope! The bugs are not going to decimate your entire garden (despite how it may feel!).

So what do we do? First, don’t panic! Seriously, in the grand scheme of things, a nibbled petal is not really a big deal. You may roll your eyes and say I know— But you wouldn’t believe how upset I see some people get over a chewed petal.

Second, you gotta’ figure out what’s eating it? Inspect your plant, turn over the leaves, look carefully between all the layers and see if you can find the culprit. Also notice what might be flying around the plant . Often times, the culprits will fly up when you ruffle the leaves.

Take pictures of the damage. I find that if I need to Google to figure out the culprit that a picture is better than my memory.

No sign of anything? Then there are a few culprits who you don’t see but they love a tasty petal or leaf. Slugs are a big one, especially on new growth or the sprouts just as the dahlias are peaking out of the ground.

Grasshoppers— if you see petal damage where it looks like something just took a dull knife to several petals at once and chopped them off- probably grasshoppers.

Are your dahlias turning brown especially where the petals meet the center? Most likely thrips. Thrips are very small brown bugs which are hard to see but cause loads of damage- they really like white/pastel colored dahlias. If you think you might have thrips, but aren’t sure- shake your flower over a white piece of paper. The thrips will fall out and be brown specks.

Cucumber beetles are another common pest. A lot of people grow vegetable gardens near their dahlias. Cucumber beetles love dahlias and anything in the squash family. The squash family (cucurbits) attract the beetle and then it finds its way over to your dahlias and has dessert from your pretty cafe au lait petals! Cucumber beetles can be very devasting to a dahlia field. So much so that I’ve stopped growing anything in the cucurbit family within 100 yds of my dahlia field. This practice has significantly reduced the number of cucumber beetles that I see each year.

These are a lot of the common pests that do visible damage to dahlias. However there are some that don’t appear to be hurting anything because they don’t chew but can be very detrimental to your plants.

Leafhoppers are one. They are small green bugs that hop from plant to plant. They do suck sap out of your plant. Leaf hoppers are a vector insect- which means that if a dahlia has a disease/virus etc. they can carry it to another plant. So while you may not see much visible damage from leafhoppers, they can be very detrimental, especially if you are growing a high number of plants.

We’ve identified a lot of the common pests that plague our dahlias- so what do we do about them?

The answer to that is coming up in our next article because this is too much for one post!

If you are having issues with a pest that we didn’t name here, see if you can get a picture of the pest or the damage and send it our way! You can submit it here.

The Pros and Cons of Early Dahlias

Last week I was sitting around with some farmer friends and we started talking about dahlias— cause it’s almost that time ya know? A few growers mentioned how they had left their tubers in the ground to overwinter and thus began a discussion on the pros and cons of early dahlia blooms. It was some good stuff so I thought I’d share what we talked about!

First off— who doesn’t want to see their dahlias earlier rather than later? So point #1 in the pro category. In order to get earlier blooming dahlias, you need to either overwinter (if that works for your zone), plant very early, or pre-sprout and pot up indoors. Any of these methods would bring dahlias on early. In my zone 7b climate, early dahlias are usually blooming mid- June. If you plant after our last frost date, then usually mid July for first bloom. If you are warmer or colder, adjust accordingly. A lot of this info is a bit more specific to warm hot climates but from what I know- if you are colder, then early blooms wouldn’t be much of a thing without a temp controlled greenhouse.

I really think it’s a matter of expectations if you are going for early blooms. I know some people do it intentionally but I suspect most folks just don’t want to have to dig them up in the fall (and I don’t blame you!).

So in the con category- early blooms are way more susceptible to pest problems. June brings thrips and Japanese beetles in my area. Might as well go ahead and add in the grasshoppers that will be in by late June and well you can forget about getting a perfect bloom without an organza bag!

Also in the con category- vase life! Dahlias that bloom in hot weather have an average vase life of 3-5 days and big dinnerplate types- You might as well enjoy them on the plant. Years ago I had a beautiful flush of cafes in mid- July. I thought it was going to be awesome until I started testing vase life and I was getting 3 days! That’s really not even usable for an event. So now I program my cafes to come on much later when the weather is cooler.

So where does that put us if you left your tubers in the ground overwinter? You have a few options.

1. You can accept the pest pressure and realize the first blooms are not going to be perfect unless you bag them or spray them but honestly a lot of sprays won’t get the thrips.
2. If you sell your blooms, advise your customers of the shortened vase life. I think this is pretty important because you don’t want to turn people off of using dahlias in arrangements. I make sure to let my customers know the vase life gets better in the fall and that summer dahlias should be used for events only!
3. You can cut your plants back. This is a good option if you want to minimize the work of dahlias and overwinter them. In mid june or when you start seeing buds, cut the plants back by half. You can also use this technique to time out blooms too. On average it will take the plants 6-8 weeks to rebloom if you cut back hard. The exact time depends on the variety.

All in all I don’t think having early blooms is a bad thing but I think it’s worth having the knowledge and correct expectations of how dahlias perform differently in hot weather.

So are you ready for Dahlia Season? If you need a bit of help getting started, join us for our On Farm Workshop- Dahlia Dividing and Planting- April 23. All the info here!

Not local? Check out our virtual Workshop: Dahlia Growing in the South

The Dreaded Powdery Mildew

It may not be flashy and sexy but if you grow dahlias you are going to come across powdery mildew sooner or later. This is meant to be the layman’s guide to powdery mildew. If you want to get really geeky, there’s a Google rabbit hole you can go down, I’m sure!

A really bad case of late season Powdery Mildew

What is it?

First off, what is powdery mildew (PM)? It’s a fungus that is characterized by a white powdery growth on the upper leaves of plants. Newer growth and succulent tissues are more susceptible to PM. It can affect pretty much any type of plant however it is host specific. This means that if you see PM on your rose bush, that variety of PM isn’t going to affect your dahlia plant. Why? Because they are in different plant families. Roses are part of the Rosaceae family and Dahlias are in the Asteraceae family. This is handy information to know and helps you figure out how to arrange plants in your garden— what you can plant next to what. A quick google will tell you the plant family for a species.

PM does overwinter in soil so once you have it, you’ll be dealing with it again and again. If you grow dahlias in a hot climate, it’s a given. That’s why prevention is important. I’ve developed some ways to hold it off for a large part of my season. It can kill a plant but I’ve found that if you hold it off long enough, you can usually make it through the season without losing your dahlia. It’s not a death sentence.

What causes it?

There are environmental triggers that cause PM to show it’s ugly face. The biggest factor in a hot climate is hot and dry conditions. Often in early summer, my area goes through a week’s worth of rain (where we all worry about tuber rot) and then we will go dry for 2-3 weeks with very little rain. This period is a perfect example of conditions that powdery mildew loves! Now PM does need humidity in the air to form spores on our leaves however in my hot southern climate, humidity is still a given even during a hot dry period. Our air is naturally humid enough.

Another environmental issue is airflow. PM has to have humidity to form but the humidity around your plants may be higher than what’s in the air above because your plants are closer together. Airflow is insanely important!! This is why you often see hot weather dahlia growers remove the bottom foliage off their plants. Increasing your airflow is key.

Prevention

Once you understand the conditions PM thrives in you can begin to thwart it. A few years ago, I began to use sprinklers in my field as a method of cooling the plants during extremely hot days. During that summer I noticed that my plants got hardly any powdery mildew until later in the season when it was cooler and I didn’t use the sprinklers as much. This led to a bit of research and I learned what I just shared above about PM environmental triggers. Keeping a “rinsing” once a day on the leaves kept the spores from having time to form. So now I set up sprinklers that cover my field in late May. I run them for 20-30 minutes daily. Sometimes a bit longer if we are extremely hot and dry. The sprinklers are the best method I’ve found for PM prevention and it’s rather organic!

Another aspect to note is that certain varieties are more susceptible to PM. Dark leaf dahlias always get it first! Which is a shame because I love dark leaf varieties. I’ve also noticed some varieties have great resistance to it. Looking at you Ice Tea!

Ice Tea Dahlia

Treatment

The old saying of “an ounce of prevention is worth a pound of cure” is most definitely true when it comes to PM. However, you may get to the point where water is not cutting it. There are some tried and true ways to deal with it. Sprayed fungicides are the surest way to deal with PM. However, you do have to spray regularly once you start. I hate having to spray 2000+ plants which is why I’m big on prevention. Copper fungicide is my go to. Whatever you use, apply it according to the directions on the label. Also remember- Don’t spray during the middle of the day. Only spray when it’s not windy and the sun is not directly on your dahlias. I prefer evenings so that the spray has time to absorb into the leaves without any risk of burning.

A few other things- If you see PM on a few leaves, remove them from your plant. Do Not Compost. Dispose of in your trash or remove them from your property. Even with prevention methods, you’ll eventually see a few spots but if you can remove them before they spread, it’ll keep the disease down longer. Scouting your plants regularly is important. That is one side benefit to spraying— you get time to look at your plants!

Also be careful of late season nitrogen fertilizers. You shouldn’t be fertilizing dahlias with nitrogen late in the season anyways, but this applies to other types of plants too. The new growth is especially attractive to PM. If you live in a climate where you cut dahlias back in mid summer, pay close attention to removing your plant debris from your field if you’ve already seen PM that season.

Summer cut back of Rock Run Ashley

Based purely on observation, I do feel like growing dahlias in landscape fabric has slowed the spread of PM too. The fabric blocks the migration of the spores from the soil. However, I do think it’s a good idea to clean your fabric if you re-use it.

Same bed 6-7 weeks later, clean and healthy ready for re-bloom

Winter is a great time for thinking about disease prevention and how to deal with pests. Take this time to get your game plan for a successful dahlia season!

Winter Dahlia Care- Part 3

Part 3 of our Winter Dahlia Care series- Storage and Monitoring