by Sally Colby
Erin Lizotte, IPM educator at Michigan State University, says scouting involves monitoring a crop and looking for problems. “It’s being out there and being aware of what’s going on,” she said. “We begin scouting as soon as plants begin to grow or when pests become active, and continue to monitor the crop until it’s dormant or until the risk of the pest has passed.”
Lizotte says one of the mistakes that’s been made in Michigan, where hopyards are just becoming established, is growers believing that pests are no longer a threat after the hops are harvested. “What we’ve found is that there are issues that can occur post-harvest,” she said. “There are some treatment windows for some of the pests, so post-harvest scouting is just as important as early season scouting.”
It isn’t enough to determine which pests are in the yard, but how many there are and how much damage are they doing. Scouting also helps determine the life stage of the pest, which is critical information for making management decisions. “We’ve moved from a lot of broad-spectrum insecticides to more narrow spectrum insecticides that have to be timed accurately,” said Lizotte. “Are we looking for something that controls eggs, or something that’s effective on adults?”
Post-application scouting is also important — it helps the hopyard manager determine whether the issue was resolved completely, to what degree it was resolved or whether there a new infection or infestation.
“Scouting includes monitoring the crop for signs of disease,” said Lizotte. “It also might involve quantifying the incidence (how many plants are affected) and severity (how severely are those plants affected). For downy mildew (DM), we see leaf sporulation. It looks a lot like Roundup injury.”
Insect scouting includes a careful search for all life stages and quantifying the population. The crop should be inspected for insect damage, and if appropriate, traps should be set up to monitor insect populations. Lizotte uses the example of damage by the potato leafhopper, which is evidenced by yellowing around the leaf margin, and the presence of wingless nymphs when the leaf is turned over. “Potato leafhopper has probably been around in the yard for a while based on that insect’s life stage,” she said.
Good scouting also reveals abiotic issues, which are problems that are not the result of insects of disease or insects. ‘Weed whacker blight’, which is mechanical injury to plants, can look like insect disease damage. “Another one we see in Michigan is nutrient deficiency,” said Lizotte. “Oftentimes, it’s a pH issue. One of the first things we do if we see issues we can’t explain is a pH test.” Scouting can also reveal signs of excessive water, lack of water, plugged emitters and damage by mammals.
Lizotte describes a good general protocol for scouting, beginning with sectioning the farm into manageable sizes, and if appropriate, by variety. Many new hopyards in the Midwest and east of the Mississippi are relatively small and several varieties of various growth stages may be present in the same yard. “It’s important to break those up (into sections) for a few reasons,” said Lizotte. “There are differences in varietal susceptibility to a lot of pests and diseases, and we manage young hops differently than mature hops. When we’re thinking about how to break things up for scouting purposes, think about how you’re going to spray a section if you have an issue.”
It’s helpful to review a list of known pests and beneficials that are likely to be present prior to scouting to avoid wasting time in the yard trying to identify insects. “If biological information is available, we can use it to gauge when we might scout more intensively,” said Lizotte, adding that leafhoppers often arrive with spring storms. “There are indicators we can use that help focus our energy and attention on points of the season that are most critical for scouting.” A regional hops scouting calendar can help the grower gain awareness of what to look for at various times of the year, from early spring to post-harvest.
Growers should look at and track historical weather data as well as forecasts. As crops become more established, predictive models are useful to help forecast high risk of disease or insect emergence. Lizotte urges growers to use a combination of knowledge about pests along with past weather patterns and weather predictions to scout and make plans to manage issues in the hopyard.
When it’s time to walk through the hopyard, the recommended path is a diagonal pattern, from corner to corner, as well as the edges. “We see different issues at the edges and interior,” said Lizotte. “Along the edge, where it’s warmer and drier, we tend to see more mites. In the interior, where there’s less air flow and longer drying time, we see more disease like downy mildew.” Each time the yard is scouted, start at a different edge and change the path. If a problem is identified in one section of the yard, be sure to visit that area each time you scout.
Experienced hops growers know what to look for, but what’s important for the grower who’s just starting? “By mid-season, hops plants look pretty beat up,” said Lizotte, adding that it’s harder to see damage. “They’re on the strings, exposed to the wind, but there are some visible cues such as cupped, chlorotic, spotted or malformed foliage. Look for discolored, damaged, swollen or sunken areas, a large number of insects — anything out of the ordinary. It takes time for your eye to get used to how things ‘should’ look so you can start to identify problems.”
Move through the hopyard, gently shake the strings and look for a flight of insects, especially leafhoppers. Check leaves from all reachable heights. Remove leaves from several plants, turn them over and inspect them closely with a hand lens. The goal is to get an overall view of the yard as well as a close-up look. “I like to check leaves from the lower, more dense portion of the canopy,” said Lizotte. “It’s damper and more protected, and it’s where we see more disease and insect activity.”
Lizotte urges growers to be aware of the role of beneficial insects, predators and parasites that can help control the pest population in crops, and to learn to recognize the various life stages of these beneficials during scouting. “As research into beneficials continues, we realize how many services they’re providing in the field,” she said. “The lady beetle gnawing on aphids is the poster child for natural enemies. The lady beetle is a generalist predator that eats a lot of soft-bodied insects and larvae.”
One of the most prevalent natural predators is the green lacewing. “A lot of the adults either don’t feed or they feed on nectar,” said Lizotte. “But their larvae are predaceous. The eggs are very distinct — they’re laid on a silken stalk on the underside of leaves.”
Lizotte says many natural enemies prefer the same habitat as native pollinators. “In the last decade, there has been a lot of work on how we can create landscapes that support pollinators, which translates to supporting natural enemies,” she said. “They’re more likely to thrive in undisturbed areas that provide overwintering habitat and flowers to support their survival.” Areas such as ditches adjacent to the hopyard or a natural drainage area may be ideal for supporting natural enemies.
The Pacific Northwest Hop Handbook, available online at http://tinyurl.com/y7oy3gcw is a good a resource for managing pests appropriately. But remember that pests, the products to treat them and laws regarding such products vary from state to state.
When scouting hops the more you look, the more you see
by Sally Colby