Summer pests and diseases

Hornworm on a tomato plant.
Photo Pam Dawling

It’s August, which for us is the peak time for pest insects as well as for fungal diseases.

This year, we have been collecting Japanese beetles from our okra plants, to prevent the leaves getting stripped off. It seems to be working. Many plants can take 30% defoliation without a loss of yield, but some years, our okra plants end up as just a bunch of stalks, and you know that means almost no photosynthesis can happen. Japanese beetles are one of the insects that have an aggregation pheromone, so those commercial traps are not only gathering up your own Japanese beetles, but also attracting neighbors’ beetles. Sometimes this means no net improvement, as the newcomers eat crops before going into the trap.

Another bad summer pest here is the Harlequin bug, a brightly colored stink bug. We try to have July be “No Visible Brassicas Month” aiming to disrupt their lifecycle. We use insect netting over the fall brassica seedlings we sow in June, and we clear our spring brassicas before the end of June. In July and July we use netting over any new brassica transplants, and sowings of turnips. During August we remove netting from older transplants and sowings, on to newer ones, such as kale and collards.

Leaf-footed bug, one of the stink bugs. Photo Kati Falger

Here’s a link to an article on Stink Bug Identification and Management in Vegetables, from the Alabama IPN Communicator Newsletter. Read More

I wrote about squash bugs and cucumber beetles on our hoophouse squash in June.

Squash bug nymphs and eggs
Photo Pam Dawling

Margaret Roach at A Way to Garden has a good post on distinguishing between the tobacco and the tomato hornworm.

The tobacco hornworms, Manduca sexta, is close cousins with the tomato hornworm,

Both species eat Solanaceous crops (nightshades) such as tobacco, tomato, peppers, eggplant and potatoes. The differences are in the stripes and the horns.

We have tobacco hornworms (this land was a tobacco farm before Twin Oaks bought it 51 years ago. This year, for the first time, we haven’t had any hornworms in the hoophouse. We’ve pulled up our tomato plants in there – we only grow the earlies in there, as it’s plenty warm enough to grow tomatoes outdoors here from May to October. I might be celebrating too soon – we still have a bed of peppers in the hoophouse and I think I might have seen evidence of a hornworm at work, although I could not find the culprit yesterday.

Tomato plant badly damaged by hornworm
Photo Pam Dawling

Pictures of Tomato Spotted Wilt Virus and other tomato diseases

We’re always a bit anxious that TSWV might show up one day, but luckily it hasn’t. Meanwhile we forget what it looks like. Here’s a few photos on the Cornell Vegetable MD Online site.

And here’s a good collection of tomato disease photos on the You Should grow site.

Spotty tomato leaves. I think this is Septoria Leaf Spot.
Photo Pam Dawling

All the news is not bad! Here’s a satisfying photo:

Hornworm mother Hawk Moth trapped by a zipper spider.
Photo Pam Dawling

Zipper spider.
Photo Wren Vile

 

Time to watch for pests

The season is warming up and insect pests are jumping into action. Here’s some old foes and some new ones to watch out for, and some friends too.

Gray garden slugs, Deroceras reticulatum, with chewing damage and slime trails on leaves.
Photo UC IPM

Slugs and Snails

We have very few snails, and compared to some other places I’ve lived, few slugs. But the slugs we do have really like the hoophouse. I found two this morning on the cucumber plants. (It was an overcast morning – they don’t like high temperatures.) My reaction was to flip them onto the path and stomp on them. We rarely have to take stronger action. If we do, we sink shallow plastic dishes into the soil, with the rim at soil level and fill the dishes with a dilute version of beer or soda, or sugary water. I don’t know if it has to be fermenting to be attractive to slugs, but any sugary liquid in our hoophouse warmth is going to start fermenting after a day. If numbers are really high and damage is extensive, we need to hunt the slugs down. Do this at dusk or later, with a headlamp and either a pair of scissors or a bucket of soapy water.

There is a good blog post by Joe Kemble on the Alabama Commercial Horticulture website:

Slugs or Snails in Your Greenhouse or High Tunnel? What Do I Do?

The post helps us understand our foe:

“Slugs are very sensitive to ambient temperature and can detect temperature changes as gradual as 2°F per hour. Slugs prefer to remain at 62 to 64°F although they lay eggs and develop normally (but slower) at lower temperatures. Development ceases below 41°F. Slugs can withstand slight freezing temperatures although their tendency to take shelter in cold weather protects them from freezing. Slugs try to escape from temperatures higher than 70°F. “

Joe Kemble offers  4 approaches to dealing with them: trapping, hunting, iron phosphate (Sluggo) and metaldehyde bait. Metaldehyde works very quickly, but it can poison and even kill dogs, cats and other mammals that might feed on it. So I don’t recommend that! Iron phosphate is much safer but also much slower – snails can take up to seven days to die. Neither should be used near waterways. Use of Sluggo has been allowed if conditions leave no less toxic option, under the National Organic Standards since 2006

Another good resource is the UC IPM site which takes the IPM steps one at a time and applies them to slugs. How to Manage Pests/ Pests in Gardens and Landscapes/ Snails and Slugs which has good photos.

Grow Smart Grow Safe  looks at many options. See their Table of Molluscicides. It explains all the current options.

Jumping Worms

Invasive Jumping Worm
Photo Wisconsin Department of Natural Resources

A new troublesome  invasive earthworm has arrived from East Asia. Here is a handy ID card

“Jumping worms (Amynthas spp.) dwell on the soil surface and eat leaf litter.  They can turn up almost anywhere from urban parks, to suburban backyards, to rural forests. Because they reproduce on their own, a single worm can start a new population. You can help prevent jumping worms from spreading to new areas by knowing what to look for.”

The Wisconsin Department of Natural Resources has good information, including photos.

These worms eat up all the leaf litter under trees, causing desert-like conditions. The surface soil becomes grainy, with a texture like dry coffee grounds, and no longer supports the growth of under-story plants.The 1.5″-8″ worms thrash around if picked up. Visually they can be distinguished from other earthworms with a clitellum (saddle), because theirs is cloudy white and smooth.

Use the jumping worm identification card [PDF] and brochure [PDF] and watch for this pest. Report finds to the DNR or your Extension Office.

————————————————————————————————————–

Spotted Lanternfly.
Photo from Virginia Cooperative Extension

Spotted Lanternfly

Another invasive alien is the Spotted Lanternfly, a pretty hopper. Lycorma delicatula (White), an invasive plant hopper, has been discovered in Berks County, Pennsylvania. It is native to China, India, Vietnam, and introduced to Korea where it has become a major pest.  As well as Eastern Pennsylvania, the pest has been found in Virginia, Maryland and New York.

The red bands on the hind wings are not visible when the insect is at rest with the wings folded up over the back. It can easily blend in on tree bark. Note that the earlier stages of this pest look very different. The first nymphs are black and white, later ones, red, black and white. All stages are spotted.

Adult Spotted Lanternfly (pinned). Photo USDA Aphis

This insect has the potential to greatly impact almonds, apples, apricots, cherries, grapes, hops, nectarines, peaches, plums and walnuts, as well as these trees: maples, oaks, pines, poplars, sycamores and willows.

The signs and symptoms of a possible infestation include

  • Plants that ooze or weep and have a fermented smell
  • Buildup of sticky fluid (honeydew) on plants and on the ground underneath infested plants
  • Sooty mold on the infested plants

If you find a spotted lanternfly, report it to your Extension Office.

Click here to learn more from Pennsylvania Department of Agriculture, and here to read more from USDA APHIS.

——————————————————————————————————————–

A zipper spider on a tomato plant, catching anything that lands on its web. Photo Wren Vile

We mostly have good bugs. While working in the hoophouse this morning, harvesting scallions out of the way of advancing enlarging cucumber plants, I also found many tiny zipper spiders and their tiny webs. These will get impressively huge. We made a point of saving their egg-cases on the bows of our hoophouse over the winter.

Zipper spider egg cases overwintering in our hoophouse.
Photo Wren Vile

I also saw a tiny praying mantis, another creature whose egg-cases we make a point of storing in the hoophouse over the winter.

And I saw a tattered Monarch butterfly. I had to check the Monarch or Viceroy? Page to be sure.

Sowing kale, finishing planting cabbage, more on zipper spiders

Vates dwarf Scotch curled kale Photo by Kathryn Simmons

Vates dwarf Scotch curled kale
Photo by Kathryn Simmons

This is what we’re aiming for – healthy kale plants to feed us during the winter! I reported last week that we had got one bed of kale sown. It’s up nicely under the rowcover, so we can use some of those plants as transplants to get more beds established when we do manage to get more beds tilled and prepped. Yesterday we sowed more kale – three partial beds which had held our fall broccoli and cabbage transplants.

We have at last got our final row of cabbage planted out, so the nursery seed beds are fairly emptied out. Not entirely though. Our next transplanting job is to fill gaps in the rows. We have 8 rows of broccoli and 4 of cabbage, 265 ft long. A hundred people eat a lot of food! Meanwhile, we raked around the remaining broccoli and cabbage transplants, and sowed more kale. A bit chaotic, having beds with big old plants and freshly sown ones, but manageable. all are covered with spring steel hoops and ProtekNet insect exclusion netting made by Dubois Agrinovation., which I have raved about previously. It keeps Harlequin bugs and flea beetles out.

We like Vates as it’s the most cold-hardy kale we’ve found and we can leave it outdoors without protection in our zone 7 winter and harvest from it about once a week. One year we did try covering it with floating row cover, to boost production, but it was a sad mistake! The fibers of the polypro row-cover got snagged in the frilled crinkled leaves, which made the cooks very unhappy!

Last winter we grew some Beedy’s Camden kale from Fedco

Beedy's Camden kale. Credit Fedco SeedsBeedy’s Camden kale.Credit Fedco Seeds

It was faster growing than Vates, and the leaves are wavy rather than frilled, and some people liked a change from our usual. Rated as hardy to zone 5, it wasn’t as cold-hardy as Vates in our garden. We are growing some more this winter.

We had planned to try Blue Ridge kale from Osborne Seeds, but they had sold out by the time I tried to order. It has done well for Clif Slade at his 43560 Project at Virginia State University, where the climate is a little milder.

Blue Ridge kale. Credit Osborne SeedsBlue Ridge kale. Credit Osborne Seeds

While shopping, I bought some Black Magic kale. We have tried these Lacinato kales in the past, both outdoors and in the hoophouse, without much success. We’ve had aphids building huge colonies in the curled back leaf edges. We’ve had indifferent growth. I’ve tasted great Lacinato kales at friends’ houses, outside our region. But every few years it come time to try a previous failure again, and we have some new crew members enthusiastic about this one, so we’re giving it our best!

Black magic kale. Credit Osborne Seeds

Black magic kale.
Credit Osborne Seeds

 

 

 

 

 

 


Two weeks ago I asked if anyone knew if zipper spiders ate hornworms. I did some reading, and I think it’s possible they do. The Latin name for these spiders is Argiope aurantia. I found out that all the many, many zipper spiders I’ve been looking at are females. The males look quite nondescript. I also confirmed that the 3/4″ brownish sacs we had hanging all over the hoophouse all last winter were indeed egg sacs of the zipper spider. Each one held over a thousand eggs! Golly! This is better than science fiction! Wikipedia says prey can include not only insects, but also small vertebrates such as geckos, so it seems likely that hornworms could be on the menu. Does anyone have a good source of information? There’s a YouTube of a spider eating a hornworm. I haven’t got enough bandwidth to watch it. Let me know if it’s good.

Zipper spider on tomato plant.  Credit Wren Vile

Zipper spider on tomato plant.
Credit Wren Vile