Featured this month:
- Early June optimism
- Late June reality
- Japanese Beetle feeding behavior
- Japanese Beetles over the years
- June weather
- Stalk Borer
Early June optimism: Fruit crops were looking pretty good in early June. The blueberries began ripening ridiculously early. We actually managed to eat a handful of cherries off of our sour cherry tree, which was remarkable since we didn’t put up bird netting (on account of the cherry quantity being too low to bother). One of our young grape vines was setting nice clusters, and the blackberries were heavily blooming and setting fruit.
Late June reality: Japanese Beetles emerged in record numbers, the worst we’ve seen in our 11 years here. And they ate (from left to right and top to bottom): apple leaves, blackberry leaves and fruit, blueberry leaves and fruit, Nanking cherry leaves (no fruit available), peach leaves (no fruit available), cherry leaves (no fruit available), gooseberry leaves, and mulberry fruit (no leaf damage so far). As of early July, there’s also leaf damage on grape, elderberry, chestnut, asparagus, and aronia. The pears, both Asian and European, have escaped damage (so far). We did fail in our intention to spray kaolin clay (Surround, a beetle irritant/repellent) on the trees before damage began. Weather and other aspects of life sometimes intervene, and it was remarkable how fast the damage got away from us this year. Later sprays did help, but a rainy forecast at the end of June and beginning of July made for some difficult decision-making regarding the efficient and effective use of time and clay.
Japanese Beetle feeding behavior: It’s not just our crops that the beetles are eating. Here’s a survey of some wild foods based on a single walk through the orchard (left to right, top to bottom: Wild grape (Vitis sp.), Winged Sumac (Rhus copallinum), elm (Ulmus sp.), Virginia Creeper (Parthenocissus quinquefolia), Shingle Oak (Quercus imbricaria), Autumn Olive (Elaeagnus umbellata), Multiflora Rose (Rosa multiflora), native rose (Rosa sp.), native thistle (Cirsium sp.), dock (Rumex sp.), evening primrose (Oenothera sp., probably Common Evening Primrose, O. biennis), and Poison Ivy (Toxicodendron radicans). Some foods are more preferred than others: Grape and Virginia Creeper are particular magnets; evening primrose typically has tons of beetles, though the specimen I photographed here was more or less empty. Some plants seem to get nibbled if they’re in close proximity to another favorite food (or one that has been depleted); for example, look at the skeletonized grape leaf next to the beetle on Poison Ivy.
We’ve been observing patterns of beetle herbivory, trying to understand what draws them to certain locations. Even among favored wild foods, some individual plants have remained relatively untouched. Why? Random chance may play a role in what the beetles find first. Sun exposure may matter, as beetles tend to feed in places with at least some sun: forest interiors aren’t their favorite hang-outs, though this year the forest floor reveals where they’re spending time in the canopy by the black droppings littering plants (normally below trees supporting large grape vines).
We’ve always been under the impression that the beetles themselves attracted others, but according to this abstract, it seems that the release of feeding-induced plant volatiles can especially draw them in, and this really seems to fit our observations. For example, one blueberry bush, and one quadrant of an apple tree, both of which were hit early by beetles, have continued to draw dense beetles even after clay application, while the nearby undamaged leaves are left mostly alone. In this theory, initial feeding starts the flow of volatiles from the damaged leaves, which draws in more beetles regardless of other factors. Removing the beetles doesn’t immediately stop the flow of plant volatiles, and so new beetles arrive no matter how many are crushed or knocked off. This also fits our theory (and unsuccessful goal) that getting clay sprayed on the plants BEFORE the beetles get bad is the best way to stop them. A key unknown is how long the plants continue to release volatiles after feeding temporarily stops; as noted above, beetles continue to flock to damaged areas for a day or two even when clay renders the leaves unpalatable. Would removing damaged leaves from plants help reduce the attraction?
Japanese Beetles over the years: June is early for beetles to appear in problematic numbers. A survey of our blog archives shows that 2012 was the only other year with notable emergence beginning in June, and that year also had a particularly warm and early spring. The continued intensification of the beetle outbreaks over the years is pretty apparent based on these excerpts:
July 2010: “at least we’re not yet within the apparently widespread outbreak of Japanese beetles south of us. I’ve run across more than one article on these horrible invasive pests affecting vegetable and fruit crops in SW Missouri, and Joanna’s parents report that they’re all over the place in NW Arkansas. Apparently their garbage man has caught 35lb of beetles in pheromone traps so far at his own place. Joanna has seen only two or three here, but someone we know reported having trouble with them near Rocheport. Fingers crossed….”
July 2010, one day after the prior post: “A day after writing that we hadn’t really seen Japanese beetles here yet, we’ve started finding them today.”
2011: no mention on the website
June 2012: “…Japanese beetles [are] an increasing threat to both agricultural & wild plants in our region. They can swarm over favored plants and defoliate them. For example, skeletonized wild grape leaves are littering the ground in some parts of the farm, thanks to the action of Japanese beetles.”
July 2013: “Japanese Beetle populations have been the highest we’ve ever experienced (though we’ve heard accounts & seen photos of much worse).”
also July 2013: “We are dealing with a significant outbreak of Japanese beetles, the largest we’ve had in our seven years here, which are attacking lots of wild plants (especially grape & rose, but even elm, shingle oak, and more) along with our apple trees, blackberries, okra, edamame, and eggplant.”
2014: no mention of Japanese Beetles (but our focus on the crops and ecosystem strayed as we dealt with the aftermath of fungicide drift that July)
July 2015: “A discussion of July 2015 beetles wouldn’t be complete without a mention of Japanese Beetles. These annoying invasives seem to be in outbreak mode this year, with the highest populations we’ve seen in our nine years here.”
July 2016: “In past years, we’ve achieved sufficient control by knocking beetles into buckets of water each morning. Not this year; we finally experienced an outbreak at a level that risked permanent damage to fruit trees, and we opted to take more extreme measures.”
This escalating infestation matches the trend noted by the Wikipedia entry on Japanese Beetles, which includes a 2006 map showing their populations mostly east of the Mississippi River, with a cryptic note that “They were present in many more sites as of July 2012.” As 2017 is already, once again, “the worst we’ve seen”, we’re forced to wonder how much worse it can get. We hope not much worse. Sooner or later, something ought to realize that these are an easy source of food. The chickens love them, but beetle predation by wild birds seems to be light. Assassin bugs take a few. Two parasitoids, Istocheta aldrichi and Tiphia vernalis, have been introduced to the United States for control, but we’ve seen no evidence–either through direct observation or web searches–that these are in Missouri. It looks like we’re in for a long period of beetle-mania.
June temperature: Compared to the temperatures June can deliver here, the month was mercifully pleasant. The highest temperature was 91ºF, and the low temperature on June 26 matched a record minimum of 50ºF.
June precipitation: The month began with a long dry spell that motivated us to get the irrigation back in operation. It ended with the kind of weather that causes irrigation to be overrun with weeds.
Stalk Borer (Papaipema nebris): Here’s a pest of rather minor concern. We always find this critter by noticing a wilted plant tip. In this case, it’s a young blackberry shoot, but many other plants serve as hosts, including tomatoes, peppers, and ragweed. Closer inspection of the stem reveals a hole. Cutting the stem in the vicinity of the hole reveals borer damage, and very often, the borer itself, which happens to be the larval caterpillar stage of a cutworm family moth. This Stalk Borer hits plants sporadically, usually in low numbers. They’ll kill young plants, particularly peppers in our experience, but they can usually be pruned out of established plants such as tomatoes or this blackberry, which was in need of tip-pruning anyway.
Quiz: What is this tree seedling? Even though I sprouted and planted the seed for this tree, I wondered for a time whether the seed had been eaten and instead some random weed came up. I resorted to an online search to convince myself that it was the target plant, which it is. So, the quiz to readers: What is this plant? And why is its identity confusing? Post your answers/guesses in the comments; the answer will be revealed next month. We might drop a few hints in the comment thread if needed, so ask questions if hints are desired.