Tomato Biocontrols

 

 

 

 

And avoiding the sweaty mess of spray gear in the summer is an added bonus. Regardless of the rationale, bios can be used easily, cheaply and effectively with a few phone calls in addition to a thorough scouting regimen.

 

Most growers, thankfully, only encounter one or two of the pests that can decimate tomatoes in hoop houses or greenhouses. They likely lock horns with these same critters perennially, and there’s always the possibility of developing new pest problems. That’s what makes a grower’s life interesting, anyway. Roughly speaking, the key pests of tomatoes are aphids, thrips, spider mites and whiteflies, which commonly rear their ugly little heads in the same order. There are no guarantees with pest control, so it’s a loose chronology. But before we go into too much detail about ways of killing them, a brief interlude about sanitation.

 

We’re all tired of hearing about the importance of sanitation, and I really don’t want to beat a dead horse. That said, the severity of your pest problems this year is tied to the amount of pests you have carried over from last year. Aphids and whitefly persist often at undetectable levels on weeds and greens, spider mites stay dormant on debris and structures and thrips live everywhere—on weeds inside and near the structure or in the soil. In addition to simply cleaning your hoop houses and greenhouses, consider solarizing them too. Simply close everything up between crops and let the sun bake the house for a week or so. That’ll kill many of the pests that were hanging out on your previous crops. And if you were growing any winter crops, chances are those pests are aphids.

 

For aphid control, Aphidius parasites are your first responders; call your biocontrol supplier at the first sign of aphids. Aphidius are little wasps that lay their eggs inside young aphids. Those aphids continue to live and grow for another 6-10 days, after which they swell into a golden brown, papery aphid “mummy.” Seeing as the most common aphids encountered on tomatoes are green peach and potato aphids, the two parasites involved here are Aphidius colemani and A. ervi, attacking the former and the latter aphids, respectively. The 2 mm long A. colemani completes its life cycle in 2 weeks, while the 4 mm A. ervi takes a week longer. Though they develop more slowly than their aphid hosts, one female wasp can kill hundreds of aphids.

 

Judson Reid, the Senior Extension Agent with Cornell University’s Vegetable Program suggests, “Once temperatures are dependably above the 40s (F), I like to release a mix of [Aphidius] parasites.” Aphid parasite mixes are more expensive than those targeting a certain species, but Reid says “We lose too much time trying to get the aphids identified.” But with a good shot from a smartphone camera, some savvy growers can get an ID the same day. Aphid parasites are shipped inside their mummies, so keep the vial closed until you see that some wasps have emerged. Release at least one wasp per 10ft2 weekly or biweekly (depending on temperature and aphid population) three times. As with many winged bios, these wasps are attracted to bright lights and should be released at dusk.

 

By April and May, the aphid midge, Aphidoletes aphidimyza, is a useful compliment to the slower-acting parasites. Released at a rate of 1-10 midges per 10ft2, for three consecutive weeks, the midges can bring even established aphid populations under control. Not surprisingly, the more aphids you have, the more midges you should plan on releasing. If your aphids are under control by June, usually enough predators will join the party from outside to keep cool weather-loving aphids under wraps until frost. Of course, the warm season brings plenty of its own challenges.

 

With warmer temperatures, the life cycles of other pests like thrips speed up, allowing even low populations to explode seemingly overnight. But don’t worry. They’ve got a bug for that. According to Judson Reid, “I would suggest people start with cucumeris. And treat transplants in the propagation house rather than after planting out. It’s inexpensive enough to use preventatively, and it’s likely to provide sustained control.” Reid goes on to say, “Two releases of cucumeris has been enough to knock our thrips population down to undetectable.”

 

Cucumeris are predatory mites that arrive amongst wheat bran, which hosts a prey mite that the cucumeris eat until they disperse get onto plants. These predators are not picky eaters, but they eat newly-hatched thrips, the only thrips life stage small enough for the little mites to tackle. When thrips hatchlings are scarce, cucumeris will munch on pollen, broad mites and spider mite eggs, allowing predators to establish long-term. You’ll want to release them at least twice at two week intervals. Once sprinkled onto the foliage, the mites disperse out of the bran on their own.

 

To be on the safe side, you can release rove beetles (Dalotia coriaria) or the predatory mite, Stratiolaelaps (=Hypoaspis), which will eat thrips when they drop to the ground. The former, being flight capable, can colonize large areas quickly and are used for structures with soil or gravel floors. Stratios are more useful for localized introductions like tomatoes grown in bags of media or in seedling trays. Both critters are introduced only once, at planting and will remain all year. Just sprinkle them on the soil near the plants at a rate of 2 beetles/10ft2 or 12-25 mites/ft2. Because adult thrips live as long as 4 weeks, you will continue to see them for a while after introducing bios, but the skies start to clear thereafter. Once your thrips controls are in place, it’s time for an even mitey-er task.

 

I’m speaking, of course, about spider mites. Difficult to detect on hairy tomato leaves, mites can explode to biblical proportions during a week of hot, dry weather. Rather than straining your eyes looking for mites on your tomatoes, try some indicator plants, those plants that show pests early and easily. Bush beans are cheap and easy indicators for spider mites. Tiny, white pinpricks (stippling) are clearly visible on the upper side of the leaf, so monitoring the beans is a cinch. One bean plant per 200ft2 is plenty. You’ll want to have them up and growing by mid-late April, or a few weeks before you’ve historically spotted your first mites. Then watch those bean leaves for spider mite damage.  If you released cucumeris earlier in the year, you may not see any spider mites at all, but luck favors the prepared.

 

As always, make the call to your biocontrol supplier at the first sighting. “If someone had a mild spider mite problem, I would recommend several releases of Persimilis,” suggests Reid. Persimilis are predatory mites that can stick around long-term, provided the beans continue to host spider mites. You’ll want to release them at a rate of one mite per ft2 every week at least twice. After the predators establish, it’s likely that you won’t be able to find spider mites anywhere but on the beans, as the predators pick off the few spider mites they find on the tomato. The bean plants are a great place to assess the number of spider mites per predator and decide if the predators are in good balance with the pest. Predatory mites are distinguished from their prey by their teardrop shape, cream to red coloration (never green) and their speed. They zip around on the leaves while spider mites move slowly, if at all. Generally, a ratio of 10 spider mites per predatory mite is safe, while 20 spider mites per predator indicates another predator release is in order. Keep your eyes on the lower leaves, where spider mites are most numerous, along with our last pest (finally!), whitefly.

 

Whitefly adults, with their erratic flight patterns and habit of flying up people’s noses, often catches the scout’s attention before translucent green immatures. If you catch them right out the gate, the prognosis for biocontrol is good. “It’s so easy,” says Carol Glenister, owner of IPM Labs, a biocontrol supplier. “It’s just four weekly introductions of parasites at the first sign of whitefly. It’s inexpensive, it’s fast and it’s effective.” So there you have it. Release one wasp (Encarsia formosa) per ft2 at each introduction and you’re good to go. Just like with spider mite predators, check the pruned leaves before discarding them. Whiteflies with parasites developing inside turn black, so any leaves with blackened whitefly pupae should remain on the plant for several days longer. And speaking of longer, this article is long enough. Time for some take-home points.

 

Perhaps the biggest shift when shifting to biocontrols needs to happen in your mind. Bios will not eradicate pests, nor should you want them to. They provide gradual and constant pressure on pests, keeping pest levels at consistently low levels. So expect to see a few unwanted visitors every so often, especially when they start coming in from outside. Calming the knee-jerk reaction to any pest sighting is a slow process, but you’ll relearn what thresholds work for your biocontrol program pretty quickly. Should pests exceed that level, you’ll need to use other tools at your disposal.

 

Pesticides and bios are not mutually exclusive. In fact, due to the increased adoption of integrated methods, many new pesticides are target-specific and compatible with many beneficial critters. Check with your biocontrol supplier to ensure that your chemicals are biocontrol-friendly and if their use is warranted. Keep in mind that chemical control takes back seat to biological control once adopted, and should be used as a last resort. But you can rest assured that this isn’t your biocontrol supplier’s first rodeo. Because tomatoes are such widespread high value crops, tomato biocontrol has been fine-tuned over many decades, and we know what to expect by this point.

 

For most growers, not needing to sweat it out under layers of Tyvek® and respirators is not a tough sell. Talking about your biocontrol program resonates extremely well with the public, especially given how educated and inquisitive consumers have become about their food. Bumble bees will buzz your praises, while naturally-occurring beneficial insects, including pollinators, will become more abundant through the year. Over the course of the year, you’ll see healthier, more robust and productive plants, as they won’t be stressed by spray phytotoxicity. And finally, your wallet, especially when labor and equipment costs are factored in, will be healthier and more robust too.