Weather dictates disease and insect control measures

 

    During the last 5 days of June it rained every day for a total accumulation of over 5 inches. With all that rain, the Neosho river spilled over its banks and flooded my pecan grove. The excessive moisture provided excellent conditions for the spread of pecan diseases but I was forced to wait until the flood receded before starting up the sprayer. While waiting to spray a fungicide,  I also noticed several colonies of Japanese beetles (photo at left) starting to feed on pecan leaves. 

      Japanese beetle has been a pest in the US for also 100 years and has moved slowly westward across the continent. For SE Kansas, Japanese beetle is a new pest that I first noticed only 5 years ago. This year, the beetle population has grown large enough to present a significant threat to pecan foliage.

 

   The damage on pecan is easily spotted high in the tree's canopy. Beetles feed on foliage in large groups leaving areas of tree canopy with a lace-like appearance (photo at right). This photo was taken a few hours after an insecticide and fungicide application so the beetles are gone but evidence of their activity remains. I just wish I had a way to capture the wild buzzing of beetles around the tree when I hit them with the air-blast sprayer. While driving the sprayer a blistering 1.9 MPH, I was able to get a pretty good feel for the large number of beetles that had been feasting on my trees. 

   During the morning of spraying, I also noticed a single fall webworm colony (photo at left). The insecticide I used to control Japanese beetle will also kill the larvae inside this single web. However, the appearance of this webworm colony serves as a reminder that I will need to stay vigilant with my pecan pest scouting efforts.

    Starting at sunrise this morning (3 July 2021), I sprayed my orchard using Quilt fungicide and Mustang Maxx insecticide.

 

 

 

Insects feeding on pecan leaves

    Over the past week I've been scouting my pecan orchard for signs of summer foliage feeders.  At this time of year, we can have outbreaks of Fall webworm and/or walnut caterpillar and I don't want to be caught unaware. 
    I did not find any colonies of  either species of caterpillar in my orchard but spotted several Fall webworm nests on roadside trees (photo above).

  Fall webworm colonies are the easiest to spot because they spin a white web over the entire colony designed to protect the caterpillars inside from birds and predacious insects. In the close-up photo at left, you can see numerous Fall webworm larvae clustered in the center of the web. These larvae will move to the margins of the web at night to feed on green foliage and spin silken threads to expand their web.  Once the larvae reach full size, they will drop out of the web, fall to the ground, and pupate in the leaf litter.  The colony of webworms I spotted this week represent the first summer generation. A second and often larger generation will appear in late August.

    While I collecting leaf samples this past week, I also spotted a few Japanese beetles feeding in my trees (photo at right). The Japanese beetle is an introduced pest that has moved steadily across the US since first landing in New Jersey in 1916. I've seen it sporadically on my farm for the past 3 years. Last year, a large colony of Japanese beetles practically defoliated a young sweet cherry tree in my fruit orchard before I sprayed the tree with an insecticide.

   I have yet to see large numbers of beetles feeding on my pecan leaves. For the most part the damage has been minor and not damaging enough to warrant pest control measures. The photo at left illustrates the light feeding damage I found on one tree in my grove. This insect seems to scrape off the surface of a leaf until it finds soft leaf tissue between the veins. At that point, the beetle eats through the leaf blade leaving an irreagular shaped hole.
   I don't think Japanese beetle will become a major problem in commercial pecan groves where insecticides are applied regularly to control major nut-feeding pests.  

Making my third disease control spray

    This summer had been wet and humid in SE Kansas. Pop-up thunderstorms have been frequent and those wet spots in the pecan grove never seem to dry up completely. Needless to say, this has been an ideal year for the spread of pecan diseases. Today, I was out looking at some un-managed pecan trees and I found a tree with a terrible case of pecan scab (photo at right). With an infection this bad in early July, I can guarantee you that these nuts will never yield salable pecans in the Fall. Spraying pecans with a well established scab infection like the one pictured will not cure this disease. Fungicides are only effective in preventing disease infection. This is why I've tried to stay ahead of scab this year by making multiple fungicide applications.
    I made my third fungicide application today.

    Insect pressure on our pecan trees in the area has been light. Today, I noticed my first Fall webworm colony (photo at left). The dirty white web located near the bottom of this native tree's canopy contains larvae from the first summer generation of Fall webworm. A second generation usually appears in August at a time we are often spraying for pecan weevil.

Spraying for scab

Spraying pecans (view from the tractor seat)

   With over 3 inches of rain falling over the weekend, it is high time we quit waiting on pecan nut casebearer and start concentrating on controlling pecan scab.  Today we fired up the sprayer and applied some Quilt Xcel fungicide. We sprayed the grove with our air-blast sprayer that applies roughly 100 gallons of water per acre of trees.  That makes figuring out how much chemical to put in the tank pretty easy.
    Read any chemical label and you'll find the rates of application given in amount of product per acre. Our sprayer has a 500 gallon tank or enough water to cover 5 acres. To determine the amount of product to be added to the spray tank, I just simply multiply the per acre rate by 5.  The recommended application rate is for Quilt is 14 oz. per acre. In filling our sprayer, I added 70 oz of Quilt to the spray tank.
   One word of advice abound spraying fungicides. Good disease is only achievable when the fungicide covers all plant surfaces. To get good spray coverage I always spray each tree from both sides. You should not assume that your air-blast sprayer is powerful enough to penetrate the entire canopy from just one side of the tree.

   We did include a insecticide in with our fungicide spray. We added Govern insecticide to the tank to control this summer's first hatch of fall webworm (photo at right). In scouting the orchard, we have found several colonies of first instar larvae. At this point in the webworm's live cycle they have done a minor amount of defoliation or have yet to hatch. Spraying an insecticide now should keep this insect out of our orchard until the second generation arrives in mid-August.   

Fall webworm females laying eggs to start second summer generation

    I was mowing my pecan grove  when I spotted a female fall webworm moth laying a cluster of eggs (photo at right). This egg mass represents the start of a second generation of caterpillars that will create a large white web in the canopy of a pecan tree.
    In our pecan orchard, we will not be applying an insectide specifically aimed at controlling fall webworm.
We will be spraying our pecan trees for stink bugs this week and for pecan weevil later in the month. These sprays will also serve to keep fall webworm populations under control.
    Unsprayed trees will see numerous fall webworm colonies by late August.

Hickory shuckworm, fall webworm and scab: Time to spray again

   I've been watching the weather and monitoring our pecan grove trying to keep to top of possible pest problems. I'm really worried about scab get started on our nut crop. Scab infections can spread rapidly on pecan shucks during the period of rapid nut growth that occurs during July. We have received numerous rain showers since the last time we made a fungicide application and the time has come to apply another protective layer on fungicide on the nuts (2 weeks between sprays).

 

    In scouting our pecan grove, we've seen three insect pests that I would like to keep under control. The first is fall webworm (photo at left). We don't have an overwhelming webworm problem in the orchard but there are just enough first generation colonies that, if left untreated,  may lead to a huge second generation problem in August.
  

    We have also collected several dropped nuts damaged by hickory shuckworm  You can identify hickory shuckworm damage by finding an ovipostion scar surrounded by a ring of white insect scales (photo at right). With a low to moderate crop this year I want to make sure we hold onto as many nuts as possible. Controlling hickory shuckworm will help maintain the current nut set.

    The third insect pest we have found in our pecan grove this week is Japanese beetle. This is a new pest for us and one that is just starting to move into our area. This shiny green beetle with copper-colored wing covers, usually feeds in groups of several beetles. Pecan leaves take on a tattered appearance following beetle feeding.
   In spraying for pecan scab today, we included an insecticide in the spray tank to make sure we keep webworm, shuckworm, and Japanese beetle under control.

First generation fall webworm hatching

   Today, I spotted a newly hatched colony of fall webworm larvae on a young tree (photo at right). The larvae are so small at this time that are unable to chew up the entire leaflet. Instead, these newly-hatched larvae simply scoured the surface of the leaf turning it light brown in color.
    The larvae have already constructed their dirty-white web to protect the colony from predators and parasites. In the photo, you can see that the web currently covers just two leaves. I controlled this colony by simply cutting off the two leaves, removing the entire colony from the tree, and squashing the insects under foot.
    At this point in the growing season I have not noticed many fall webworm colonies. The colonies I have seen are generally located on trees that did not receive an insecticide treatment for pecan nut casebearer 10 days ago. 

Fall Webworm outbreak

   The white webs are everywhere. Street trees, yard trees, and trees along the highway all seem to be covered by numerous colonies of the fall webworm. Last month, I photo graphed some fall webworm egg masses and predicted that we would be seeing an severe outbreak of this pest this fall. And sure enough, if you didn't spray your trees back in August, your trees are probably covered with webs.
    The photo at right shows a young tree in covered with webworm colonies. When I look at this picture, two questions pop into my mind : 1) Will webworms cause long term damage to this tree? and, 2) Why do the webs look so much bigger than usual?
   Fall webworm larvae can totally defoliate a young tree by mid-September. However, branches and dormant buds are untouched by the caterpillars. This means that limbs, defoliated in early fall, will typically remain in a dormant condition until next spring. The true long-term impact of webworm defoliation is a little harder to see.
    Losing leaves 6-8 weeks early means less time to build carbohydrates via photosynthesis and ultimately less stored energy for budbreak the following spring. The result is a weaker spring flush of growth and a slow down of tree growth rate. Fortunately, trees can overcome this lag in growth rate by supplying trees with ample soil nitrogen in early spring. 

    This fall's webworm colonies appear larger because the colonies actually have more caterpillars within each web. Over the years, I've looked at a lot of fall webworm egg masses and they always seem to be roughly the same size. This would mean the size of a colony's  web should also be about the same size each year. However, this year, there were so many egg masses laid that sometimes two egg masses appeared on a single leaflet (photo at left).  When two egg masses hatch in close proximity, caterpillars eventually coalesce and become like one big colony.  This year, I've seen young trees totally covered by webs in what looks like one huge webworm colony. However, what I'm actually seeing is the result of multiple webworm colonies competing to consume every last bit of green leaf tissue from the tree.  

Emerging fall webworms killed by insecticide aimed at pecan weevil

    During the first week of August we sprayed our pecan grove with an insecticide to control emerging pecan weevils and stinkbugs. A few days later, I reported seeing many fall webworm egg masses on the underside of pecan leaves. Actually, I found these eggs masses while spraying some young trees to control weevil. Three days after making an application of Warrior insecticide, fall webworm larvae started to emerge from their eggs. Once they emerged they contacted the pesticide and started dying. In the photo above, all the dark colored larvae have been dead for quite some time. The yellow larvae are still alive but are so sick they can't make it off the egg mass to start feeding on green leaf tissue. These larvae will die shortly.
     As it turn out, my efforts to control weevil and stinkbugs have also controlled fall webworm.

Second summer generation Fall webworm egg masses spotted

    I was mowing around my pecan trees when I spotted several dime-sized egg masses deposited on the undersize of pecan leaves (photo at right). The eggs are very light green in color but are largely covered by a layer of white fluff. This is the start of a new Fall webworm colony. Female webworm moths lay their eggs in a cluster on the underside of a leaf then cover that egg mass with scales rubbed off of the moth's abdomen. The female moths cover their egg masses in this way to hide the eggs from egg parasites.

   Driving down the highway, I noticed that the 2015 spring brood of fall webworm on roadside trees was fairly large. And judging from the number of egg masses I've already seen, the fall brood will be even bigger. I even found two egg masses on a single pecan leaflet (photo at left).
   With recent rains, pecan weevils have started to emerge and we have already sprayed the pecan grove to control weevils and stinkbugs. It looks like our pesticide application will also help keep webworms in check. Additional weevil sprays later this month should control any additional webworm colonies that arise from egg masses deposited later in August.

Fall webworm: Nobody's home

    Driving down the highway you'll see numerous webs up in trees all created by Fall webworm larvae. These caterpillars are general leaf feeders that colonize numerous hardwood tree species including pecan, hickory, black walnut, persimmon, and green ash. If you get up close to one the the dirty white webs, you will note that all the foliage inside the web has been devoured by the caterpillars (photo above). Leaves outside the web are still green and untouched. 

    By late July, all of the webs have been vacated. A closer look into the web will reveal nothing but the white fuzzy exoskeletons discarded by molting caterpillars and black balls of insect frass (photo at left). Once the caterpillars reach maturity, they drop out of the web and settle down in the leaf litter on the ground. The caterpillars then spin a cocoon to begin the process of changing into an adult moth.
   At this point in time we are between generations. The second summer flight of fall webworm moths usually starts in early to mid-August. Judging from the number of first generation colonies I've seen up and down the road, the second generation should be ever larger.  Fortunately, we will be spraying our trees for stinkbugs and pecan weevils during the month of August and these sprays will keep the second generation out of our pecan grove.  

Fall webworm makes an appearance

    While scouting our trees for pecan nut casebearer we have discovered a few new colonies of fall webworm (photo at right). This is the first of two generations that will make an appearance during the growing season. A second generation will hit in mid-August.

    Fall webworm caterpillars always appear in a large group and surround themselves in white webbing. The spinning of the web starts immediately after egg hatch. In the photo at right, a recently hatched webworm colony has eaten all the green tissue from the terminal leaflet and covered that leaflet in webbing. These insects web over the area in which they are feeding to protect themselves from potential predators and parasites. As the larvae grow in size, the amount of leaves needed to support the colony increases and the size of the web grows. 

    Female webworm moths lay their eggs on the underside of pecan leaves. The dime-sized egg masses are covered with white, fluffy scales deposited by the female to confuse egg parasites. In the photo at right, I've  turned over the leaf pictured above so you can see the remnants of the eggs mass. At the tip of the brown leaflet the white fuzzy stuff left behind after the eggs have hatched.
   At this time, it it two early to tell if we'll see an outbreak of these insects this summer. We will need to keep watching.

Webworm moths laying eggs

   Today, I found the first indication that the second generation of fall webworm is on its way. On the underside of a pecan leaflet, a female webworm moth was busy laying a large cluster of eggs (photo at right). As you can see, the adult moth is white and about 3/4 inch long. The female moth in the photo has almost completed laying a dime-sized egg mass (partially hidden under her wings). As she lays her eggs, she covers the eggs with scales scraped from her abdomen. This gives the egg mass a fuzzy white appearance.
    The eggs will start to hatch in about 7 days. The hatched larvae will immediately start feeding on pecan leaves and spinning their protective webbing. Based on the size of the first summer generation, we will start to notice a large number of new webworm colonies by the end of August.

Fall webworm colonies becoming obvious

    Driving along the highway, I've started to notice numerous colonies of the Fall Webworm. Webworms create a white web around their colony of 30 to 100 caterpillars (photo at right). The web serves as protection against both predators and parasites. Each evening the caterpillars work to extend the web further out into the canopy to capture fresh green leaves to feed on. The webs we are seeing now represent the first summer generation of the fall webworm. A second generation will appear in late August to early September.

   If you look closely inside the web, you will see an army of yellow to rust-orange caterpillars feeding of pecan leaves (photo at left). At maturity these caterpillars will grow to 1.5 inches long and be covered with long white hairs. Eventually, larvae leave their protective web and drop to the ground. The caterpillars will then crawl into ground-cover litter and pupate. A white moth will emerge from the pupal case and fly up into the trees to initiate a second summer generation.
   Many folks believe that they need to penetrate the web with an insecticidal spray to control this pest. Since the caterpillars are continuously expanding their web in a quest for more green leaves, applying an insecticide on the foliage surrounding the web will effectively control this pest.
    In commercial pecan groves, there should be more than 5 colonies per acre to justify an orchard wide insecticide treatment. This spring, I have seen very few webworm colonies in pecan groves that were sprayed for pecan nut casebearer. It seems that the residual action of the earlier applied insecticide treatment has kept early-hatch webworms in check.

Fall webworm hatching

   Last week we found an egg mass of the fall webworm. This week we found hatched out larvae feeding comfortably in their loosely spun web (photo at right). Just like newly hatched walnut caterpillars, first instar fall webworms do not have large enough mouth parts to bite through an entire pecan leaf. Instead these young larvae just scrape off the outer layer of cells on both sides of the leaf. In the photo, the leaflets nearest to the cluster of caterpillars has just been scraped clean of its outer layer. As these leaflets dry, they will turn brown just like the other leaflets under the web.
   We are not finding a large number of first summer generation webworm colonies at this time. However, since it looks like we are facing a walnut caterpillar outbreak this summer, insecticides applied to control walnut caterpillar will also control fall webworm.

Fall webworm right on schedule

     This year, pecan trees broke bud nearly 3 weeks early. First-summer-generation pecan nut casebearer came as least 2 weeks earlier than normal. So what should we expect when it comes to summer-foliage feeding caterpillars? The answer came today when I found my first fall webworm egg mass (photo at above).
    Mid-June is the normal time period for the very first webworm egg masses to be spotted. It seems fall webworm moths didn't get the memo that bud break was early in 2012.
    Fall webworm egg masses are easy to identify by the white "fluff" scattered over the top of the egg cluster. This "fluff" is actually moth scales that the female scrapes off her body in an effort to disguise the eggs to avoid attacks by egg parasites.

    By early July you should see webworm colonies in their dirty white webs (photo at left). Fall webworm has two generations per year in our area. A second generation appears in late August.
    Depending on the number of colonies we see per acre, we can control this pest with a wide range of insecticides. Currently, the action threshold for fall webworm is 5 colonies per acre. Make sure to scout your orchard carefully to spot the colonies when they are still small (the size of your fist). Young larvae are much easier to control than larvae nearing the end of their life cycle.

Summer Caterpillars

     Sometimes they seem to appear overnight, stripping the leaves from you pecan trees to satisfy their voracious appetites. Walnut caterpillar and fall webworm are easy to spot at this time of year. The first summer generation of these insects is nearing completion with a second, and larger generation staring in mid to late Augusts.
    Pictured at right are the tell-tale stripped leaves left by the feeding of a colony of walnut caterpillars. Look closely at one of the lower branch terminals and you will see a clump of caste skins left behind by the colony of caterpillars that chewed off all the leaves.

    In an earlier post, you can see a walnut caterpillar egg mass. Once these eggs hatch the caterpillars that emerge stay together in a group, eating together, molting together, and eventually dropping out of the trees together to pupate in the turf. Walnut caterpillar larvae are green when first emerging from the egg (1st instar). After the caterpillars molt, the larvae become maroon in color with log dark hairs. They keep this maroon color during the 2nd, 3rd, and 4th instars. At the 5th and final instar the large become totally black with long white hairs (zoom in on photo at left). These 5th instar larvae do 80% of the defoliation that will occur from this pest. 
     Over the years, we have noticed that walnut caterpillar populations vary greatly. Some years you can hardly find a colony while other year this insect seems to defoliating every tree in the grove. Walnut caterpillar populations are kept in check my a small parasitic wasp. In our area, the colonies we've found are small indicating that the wasp is active and working to suppress an outbreak of caterpillars. However, nut growers in Miami Co., KS and Barton Co. MO have seen much larger colonies indicating that that natural biological controls have broken down in those areas. If you have seen a large number of walnut caterpillar colonies during the 1st generation, be prepared for an even bigger 2nd generation.

   With its dirty white web, the fall webworm, can be spotted a half mile away (photo at right).  These caterpillars appear to stay within the web they create but that web is expanded every night as the larvae devore an ever increasing number of leaves.
     Fall webworm populations flucuate from year to year depending on the survival of pupae over the winter months. Warm, wet winters seem to favor the fungi that attack fall webworm pupae reducing the size of the 1st summer generation. Dry weather provides prefect conditions for insect survival so the second summer generation should prove more troublesome.