Great Lakes Fruit, Vegetable & Farm Market EXPO Michigan Greenhouse Growers EXPO

December 6-8, 2011

DeVos Place Convention Center, Grand Rapids, MI

Identifying and Enhancing Natural Enemies in Vegetables

Where: Grand Gallery (main level) Room C

CCA Credits: PM(2.5)

Moderator: Mary Gardiner, Entomology Dept., The Ohio State Univ.

9:00 am Beneficial Insects for Vegetable Production

Mary Gardiner, Entomology Dept., The Ohio State Univ.

9:30 am Enhancing Natural Enemies in Crops Using Flowering Plants

Megan Woltz, Entomology Dept., MSU

9:55 am Impact of Strip-Tillage on Natural Enemies in Cabbage

Alexandria Bryant, Entomology Dept., MSU

10:20 am Thinking Outside the Crop: Influence of Surrounding Landscapes on Ecosystem

Services in Crop Fields

Brett Blaauw, Entomology Dept., MSU

10:45 am Interaction with Speakers

Beneficial Insects for Vegetable Production

Mary Gardiner The Ohio State University – OARDC

Gardiner.29@osu.edu, http://oardc.osu.edu/ALE

In this workshop we will discuss how to identify and enhance important arthropod predators and

parasitoids. These organisms are often called natural enemies. Natural enemies provide biological control,

or natural pest control in vegetable crops. The Great Lakes Vegetable Working Group has developed a

new video with footage of important natural enemies which will be shown within this session. Attendees

can access this video on You Tube at: http://www.youtube.com/watch?v=r1EYCevAgnY

Attendees will also receive a colorful, waterproof, 2-page natural enemy identification guide and have an

opportunity to view pinned specimens of the arthropods featured in the video and guide.

Enhancing Natural Enemies in Crops Using Flowering Plants

Brett Blaauw and Rufus Isaacs, Department of Entomology, Michigan State University

Many arthropods provide valuable ecosystem services, including those that humans depend on because

they support food production. Insects have been estimated to provide Americans with natural pest

suppression services worth nearly $4.5 billion and pollination services valued at nearly $3 billion

annually. The scarcity of flowering and native plants within agricultural landscapes, the use of broad

spectrum insecticide, and the loss or fragmentation of habitat have led to a decrease in beneficial insects,

which puts us at risk of losing the natural ecosystem services they provide. Consequently there has been a

growing interest in the benefits of reintegrating natural habitats into agricultural landscapes as one

strategy for conserving beneficial insects and the services they provide. Manipulation of the habitat in

field margins or around cropped areas by establishing flowering plants and grasses can increase beneficial

insect populations in agricultural systems. Modification or enhancement of the surrounding habitat may

be an ideal approach reverse the declining natural enemy populations observed in agricultural landscapes.

Recent research at Michigan State University has identified and measured the relative attractiveness of

native mid-western perennial flowering plants that can provide season-long floral resources for beneficial

insects in agricultural landscapes. From their results, we have selected a set of herbaceous flowering

plants that rank highly for their attractiveness to natural enemies and pollinators, and are listed under the

Conservation Reserve Program - State Acres For Wildlife Enhancement. Wildflower seeds were initially

sown in early spring 2009 into plots that were prepared in fall 2008 adjacent to the crop fields.

Wildflower seeds may also be sown during the fall, which is a more natural time for seed dispersal. It is

advised to mow these wildflower plantings once a month during the first two years (alternating mowing

half of the plot each month during 2010) to control annual weed growth and facilitate perennial

wildflower establishment. The plantings should be left alone during the third year to allow wildflowers to

bloom and set seed.

The abundance and diversity of natural enemies and insect herbivores were determined in the

fruit crops using observational samples taken every two weeks from June through September.

Significantly more natural enemies per observed blueberry bush were recorded in fields adjacent to

wildflower plots (Figure 1). Insect herbivore, which may be considered pests to crop fields, showed a

trend that was opposite of that for beneficial insects, with more pests being observed in fields adjacent to

grass field margins (Figure 2).

To determine whether conservation strips lead to improved biocontrol within adjacent fields compared to

fields without this treatment, we collected leaves infested with spotted tentiform leafminers and measured

the number of larvae that were parasitized by parasitoid wasps. We found an increase in parasitism in

larvae in fields adjacent to wildflower plantings compared to fields adjacent to grass field margins (Figure

3). To further measure the effects of wildflower plantings on biocontrol, we introduced a known number

of corn earworm eggs into the wildflower plots, grass field margins, and crop fields. After four days in the

field we collected the eggs and counted the number of eggs consumed by natural enemies. In fields

adjacent to wildflower plantings there was an increase in biocontrol of corn earworm eggs compared to

grass field margins fields adjacent to those grass margins.

Figure 1. Natural enemies observed in crop fields. More natural enemies were observed

in fields adjacent to wildflower plantings compared to fields adjacent to grass field

margins.

Figure 2. Insect herbivores observed in crop fields. More insect herbivores were observed

in fields adjacent to wildflower plantings compared to fields adjacent to grass field

margins.

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Figure 3. The measured percent parasitism of spotted tentiform leafminer larvae. More

larvae were parasitized by parasitoid wasps in fields adjacent to wildflower plantings

compared to fields adjacent to grass field margins.

Figure 4. An index of biocontrol of corn earworm eggs. There was an increase in

biocontrol of corn earworm eggs in flower plots and field edges adjacent to wildflower

plantings compared to grass field margins fields adjacent to those grass margins.

Colored version: https://www.msu.edu/~blaauwb1/NaturalEnemyConservation.pdf

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Impact of Strip-Tillage on Natural Enemies in Cabbage

Alexandria Bryant (bryant30@msu.edu) and Zsofia Szendrei (szendrei@msu.edu) Michigan State University - Vegetable Entomology

243 Natural Science Building Michigan State University East Lansing, MI 48824 Phone: 517-432-0900

Lab website: http://vegetable.ent.msu.edu/

What is strip-tillage?

In strip-tilled fields, tillage is restricted to planting rows, reducing the amount of soil disturbed within the

field and reducing wind and water erosion. It can also reduce leaching of nutrients such as nitrogen and

increase soil organic matter in agricultural fields. Strip tillage can also create habitats that are favorable to

natural enemies (= predators, parasitoids) and unfavorable to pests. Strip-tillage is a management

technique that can be incorporated into current farm practices.

How can strip tillage be combined with other management techniques to improve biological

control?

When cover crops and strip tillage are used in combination, the cover crop residue from the winter or

spring is left behind in the row middles and becomes mulch for the vegetable crop that follows. In

addition to suppressing weeds and maintaining moisture, this mulch may provide habitat for natural

enemies and protection from other predators. Strip tillage can also be combined with different herbicide-

management intensities: lower herbicide intensity can increase the abundance and diversity of weeds in

row middles. Although these weeds may compete with crops, studies have shown that the presence of

weeds can increase common beneficial insect predators in cole crops, including lady beetles, ground

beetles, and rove beetles. Similarly, in an experimental cabbage field in Michigan, plots with greater weed

diversity had higher abundance of the spined soldier bugs (Figure 2A), an important predator of cabbage

pests.

How can strip tillage reduce pests and increase natural enemies in my vegetable field?

Enhancing the diversity and abundance of natural enemies can improve biological control of pests.

Natural enemies in general prefer diverse agricultural fields, where they can find shelter and alternative

food sources. In addition to attracting natural enemies, strip tillage combined with other management

practices may make row-middles less attractive to herbivores, reducing pest pressures and crop damage.

What did we find in our strip-tillage experiment in a cabbage field in Michigan?

Delaying the killing of oat cover crop in row middles in the spring allows greater cover crop mulch

biomass to remain between cabbage rows. This mulch is associated with increased numbers of both lady

beetle adults (Figure 2B) and lady beetle larvae (Figure 2C) on cabbage plants. These beetles are common

predators of the major cabbage pests: the imported cabbageworm and the diamondback moth larvae

(Figure 1A and 1B). Greater cover crop mulch was also associated with lower numbers of diamondback

moth larvae. Higher weed diversity led to lower abundance of imported cabbageworms and cabbage

aphids (Figure 1C).

Although strip tillage may form attractive row-middle habitats for generalist predators and reduce pest

populations, these row-middles do not appear to impact specialist natural enemies such as parasitoids in

our cabbage field. Parasitoids of the diamondback moth and imported cabbageworm include Diadegma

insulare and Cotesia glomerata respectively (Figure 3). This suggests that location of hosts by these

specialized natural enemies is neither enhanced nor impeded by the different management practices

examined. Specialist natural enemies such as parasitoids may actually be more abundant in cabbage plots

with less cover crop mulch and lower weed diversity, where their hosts are more abundant.

What are the applications of this strip-tillage experiment for Michigan cabbage production?

Combining strip-tillage while using cover crops and limiting the amount of herbicides can reduce

negative environmental impacts within a cabbage field. These management techniques can be utilized by

cabbage growers to prevent damage from pests such as the imported cabbageworm and diamond back

moth, which are annually occurring pests. Our strip-tillage experiment has demonstrated that techniques

such as strip-tillage, cover crop mulch, and reduced herbicide input can contribute to the management of

pest populations. However, cover crop residues and higher weed pressures reduced cabbage biomass and

leaf area in 2010 and 2011. Further work in combining IPM techniques is necessary to maintain

comparable yields and find farm practices that manage both weeds and insects.

Figure 1. Common pests in cabbage and other cole crops include A) the diamondback moth

(Plutella xylostella), B) the imported cabbageworm (Pieres rapae), and C) cabbage aphids

(Brevicoryne brassicae)

Figure 2. Common generalist predators in cabbage fields: A) the spined soldier bug (Podisus

maculiventris), B) the pink lady beetle (Coleomegilla maculate), and C) lady beetle larvae

Figure 3. A) A specialist parasitoid of the diamondback moth, Diadegma sp. and B) a specialist

parasitoid of the imported cabbage worm, Cotesia rubecula

Figure 4. Plots within a Michigan cabbage field with A) low, B) medium, and C) high levels of

cover crop mulch

Figure 5. Plots within a Michigan cabbage field with A) high herbicide intensity or both grass

and broadleaf herbicide applications and; B) and C) low herbicide intensity or grass herbicide

application alone

Figure 6. A strip-tilled cabbage field in Michigan with different levels of cover crop mulch and

herbicide intensity

Thinking Outside the Crop: Influence of Surrounding Landscapes on Ecosystem Services in Crop Fields

Megan Woltz (woltz@msu.edu) Michigan State University

204 CIPS, Michigan State University, East Lansing, MI 48824 517 – 432 – 5282

Pest control from natural enemies (i.e. predators and parasitoids) already present in the

environment provides a valuable and often underappreciated services in crop fields by preventing pest

populations from increasing and reducing or eliminating the need to use chemical insecticides. All told, it

is estimated that upwards of $4.6 billion/ yr are saved by U.S. farmers by not having to treat for pests that

are kept in check by natural enemies already present in the environment (Losey and Vaughn 2006), such

as lady beetles, ground beetles, spiders and parasitoid wasps.

However, crops can be extremely difficult places for natural enemies to survive. Disturbances

like tillage and insecticide spraying force natural enemies to seek other habitats for temporary refuge.

Similarly, many natural enemies are unable to survive the winter in crop fields due to the limited amount

of vegetation cover in crop fields after harvest. Natural enemies of crop pests also need to locate

additional sources of hosts or prey when crops are not in the field or when pests are in low abundance.

Furthermore, many natural enemies require sugar resources, such as nectar or pollen, and these can be

difficult to find in many crops.

Much of the research targeted toward enhancing natural enemy populations in crop fields has

focused on providing many of these limiting resources via habitat management, such as the planting of

floral resource strips in the vicinity of crop fields. However, increasing evidence over the last decade

suggests that the availability of these resources in the landscape surrounding crop fields is crucial for

natural enemy populations. In this context, “landscape” refers to all of the patches of different land use

types, including crop fields, non-crop areas like woodlots, and urban and residential areas, across a broad

area (Fig 1).

Fig 1. An example of a landscape, showing

patches of crop fields, non-crop habitat,

and residential areas.

For example, the abundance of spiders, lady

beetles (Fig. 2), and ground beetles in crop fields have

been shown to be higher when there is a greater amount of

non-crop habitat or a greater diversity of habitat types in

the surrounding landscape. The importance of landscape

characteristics for natural enemy abundance has been

emphasized over and over in a variety of crops, including

field crops (soy, wheat, canola, spring cereals), vegetable

crops (Brussels sprouts, potatoes), vineyards, pastures and

grazing lands, rice and cotton. Furthermore, these

increases in abundance of natural enemies have resulted in

increased predation and parasitism of pests, like Colorado

Potato Beetle, soybean aphid, Rape Pollen Beetle in

canola, and cereal aphids in wheat. In many cases, the

increases in predation or parasitism have resulted in lower

population growth rates for the pests and decreased

damage to the crop.

The types of habitats shown to be useful for

supporting natural enemies include wooded habitats like

forests and woodlots, and grassy habitats like old fields,

remnant prairies, and CRP lands. Additionally, the beneficial

habitats do not necessarily need to occur in large blocks to be

useful to natural enemies. So called “linear elements” like fencerows and grassy roadside vegetation have

also been shown to be beneficial to natural enemy populations. Importantly, beneficial habitats are not

solely limited to non-crop habitats types. In several studies, perennial forage crops like alfalfa and pasture

have been related to higher natural enemy abundances. Some options to increase the amount of beneficial

habitats around crop fields include:

Allow marginal land to be fallow and grow into lightly managed “old field”

Minimize mowing of narrow vegetation strips like roadsides, field margins and along fencerows

Plant floral habitats where possible

Diversify crops, including more spring crops like alfalfa and wheat to provide habitat in the

early in the year before summer crops are planted.

The size of a landscape surrounding a crop field that is relevant for natural enemies varies by

natural enemy species, but in general, the habitats within a circle from 0.5 to 2 mile radius around a given

field have been found to be the most important for a variety of species. This creates a difficulty of how to

manage landscapes to support natural enemies when the surrounding land may be owned or managed by

someone else. As of yet there is no good solution to this problem, but it seems likely that landscape

management to support natural enemies will rely on the cooperation of neighboring landowners. An

important first step in this process is to spread the word about the importance of beneficial habitats within

the broader landscape for natural enemies.

Losey and Vaughan 2006. The economic value of ecological services provided by insects. Bioscience, 56:

311-323.

Fig 2. Lady beetle abundance in

soybean fields increased as the

amount of semi-natural habitat

(old fields, woodlots, etc.)

increased.