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Shake Rattle & Role: BUZZ Pollination

Karl Foord, Extension Educator - Horticulture

I recently had the rare priviledge of traveling to Tucson, Arizona to visit the laboratory of Dr. Dan Papaj. I worked with Dr. Stephen Buchmann (author of several fine books) and Avery Russell to photograph buzz pollination of Solanum species flowers by the Common Eastern Bumble Bee (Bombus impatiens).

Buzz pollination occurs when an insect visiting a flower uses vibration to extract pollen from the anthers of a flower. This is accomplished by the insect activating their wing muscles without flying. This vibration shakes the anthers of the flower causing pollen to pore out the end of the anther; anthers having pores at their end are called porical for this reason.

This is not an isolated occurance as some 15,000 to 20,000 plant species have pores or slits at the end of their anthers. Also some 50 genera of bees possess the capability to accomplish buzz pollination. Interestingly enough, honey bees are not capable of buzz pollination.

Poricidal anthers are often found on flowers that also lack nectaries, and flowers that have developed anthers of different lengths facilitating pollen dispersal on the pollinating insect.

Middle C on the piano is 262 Hz (beats per second) and A above middle C is 440 Hz (the tone orchestras use to tune their instruments). The peak frequency used in buzz pollination is in between these two frequencies at 330 Hz. Buzz pollination also produces lesser peaks at the five harmonic frequencies above 330 e.g. 660, 990, 1320, and 1650.

I have produced a video of buzz pollination filmed with a high speed camera that allows one to actually see the shaking of the bee. Under normal circumstances this would only be visible as a blur. The bees were filmed at 1,000 frames per second meaning that they have been slowed down by a factor of 33.3.

Please enjoy the video!

Tomato Troubles - There is an App for That

Michelle Grabowski, UMN Extension

Wondering what is blighting your tomato plant? Looking for recommendations on how to avoid the same problem next year? The American Phytopathological Society, a nonprofit scientific organization of plant doctors, has released a new app called Tomato MD for iPhones and iPads. This interactive app helps gardeners diagnosis tomato problems with an easy to follow diagnostic key, color photos and descriptions of symptoms. Over 35 common tomato problems are covered including diseases, insects, mites and environmental and cultural problems. The app also includes an up to date list of plant diagnostic laboratories in the United States and detailed instructions on how to pack and send a sample for diagnosis. Look for Tomato MD on your device's app store.



Managing Cherry Disease Problems

M. Grabowski, UMN Extension

Photo 1:

Michelle Grabowski, UMN Extension Educator

Several disease problems have been observed on cherry trees this summer including powdery mildew and brown rot. When disease problems arise in the garden it is critical to identify what pathogen is causing the problem. There are different strategies to manage each disease and it is important to know what time of year management strategies should be applied. Many garden diseases can be significantly reduced if not eliminated with well timed cultural control strategies.

Find out more about identification and proper management of disease and insect problems of cherry, plum and apricot trees in the new UMN Extension publication Pest Management for the Home Stone Fruit Orchard.

Diseases in the Vegetable Garden

Michelle Grabowski, UMN Extension Educator



M. Grabowski, UMN Extension


Photo 1: Black rot is a bacterial disease of broccoli, cabbage, cauliflower and other brassicas.


This years frequent rains have created ideal conditions for many fungal and bacterial diseases in the vegetable garden. These pathogens need moisture to reproduce, spread and start new infections. Although gardeners can't change the weather, a few things can be done help plants dry out after rain or dew and to reduce the spread of disease.

1. Space plants to allow for air movement around the plants and through the foliage. Dense planting results in fruit and foliage that stay wet longer; a favorable condition for many pathogens.

2. Pull weeds. Weeds crowd the vegetable plant, steal nutrients and reduce air movement in the garden.

3. Completely mulch the soil with landscape fabric, plastic mulch, straw or wood chips. Many pathogens survive in plant debris and soil. Rain and irrigation splash water, soil and pathogens onto the lower



M. Grabowski, UMN Extension


Photo 2: Angular leaf spot on cucumber


leaves of the plant. Mulch provides a barrier that reduces splash dispersal of the pathogen from soil to plant. In addition, mulch keeps moisture in the soil and reduces humidity in the plant canopy.

4. Stake vining plants like tomatoes, cucumbers and runner beans. This will improve air movement around the plant and facilitate drying of the leaves and fruit.

5. Do not work in plants when leaves and fruit are wet. Fungal and bacterial pathogens reproduce under wet conditions and can easily be spread on a gardeners hands or tools at this time. Wait until plants have dried completely before working in the garden.

6. Pinch off heavily infected leaves and fruit and remove them from the garden. Many leaf spot and fruit rot diseases produce new fungal spores or bacteria in every leaf spot. These pathogens are easily



M. Grabowski, UMN Extension


Photo 3: Early blight on tomato



spread through the plant to new leaves and developing fruit. Infected plant material can be buried, placed in a compost that heats up or taken to a municipal compost facility.

Remember many plants tolerate some leaf infection and still produce a good crop. Use the steps above to reduce the spread of disease and minimize it's impact on your final harvest.

Karl Foord, Extension Educator - Horticulture




Karl Foord


Photo 1: Some of the plastic tunnels that provide optimum growing conditions on the Untiedt Vegetable Farm


Karl Foord

Photo 2: Sweet corn on Untiedt Farm

Karl Foord

Photo 3: Trellised tomatoes on the Untiedt Farm

Karl Foord

Photo 4: More trellised tomatoes on the Untiedt Farm

Karl Foord

Photo 5: Trellised cucumbers on the Untiedt Farm

Karl Foord

Photo 6: Trellised canteloupe on the Untiedt Farm

Karl Foord

Photo 7: Onions on Untiedt Farm

Karl Foord

Photo 8: Honeybee hives on the Untiedt Farm

Karl Foord

Photo 9: Protective tree barriers on Untiedt Farm


If you are not already a member of a CSA (Community Supported Agriculture), I highly recommend that you consider becoming one. To be a member one pays an up front fee and receives weekly a box of currently maturing vegetables for 17 weeks of the season. This prepayment helps the farmer to achieve better cash flow for the operation and the member/shareholder gets a greater understanding how their local food is produced here in Minnesota.

To better understand where my food comes from I attended my CSA Farmer's field day. It was an enlightening experience. Not only did I see where my food comes from but also listened to Jerry Untiedt discuss how he handles various issues such as pest control and water management. I was especially impressed with the system developed for water management. All the water that runs off Jerry's plastic tunnels (Photo 1) is channeled into a natural wet area that acts in a holding capacity. When Jerry needs the water back, he pumps it back from the wet area and waters his crops.

You can see from the photos that Jerry's soil is quite sandy. With the amount of rain we have had this spring a great deal of applied fertilizer would simply have been flushed through the system and end up in our waterways. Note the sweet corn field (Photo 2) and the green plastic under the crop. This has been placed there to avoid such a loss for the farmer and then pollution for those downstream. I was very proud to know that the food I am eating is produced in a system that has been developed to avoid such problems.

Most of the vegetable acreage is under plastic providing optimal conditions for growth. This being among others: 1) lack of rain water falling on the leaves and potentially creating disease problems, 2) protection from the stong winds that buffet and damage the plants, 3) an enclosed space permitting the use of beneficial insects to control pests - in an open field they are more likely to dispurse than protect your plants, and 4) keeping the plants within an optimum growing temperature - especially critical given Minnesota's unpredictable weather patterns.

To make optimal use of space, a number of the crops are trellised such as tomatoes (Photos 3 & 4) cucumbers (Photo 5), as well as canteloupe (Photo 6). Other crops that cannot be trellised also do extremely well in the tunnels (Photo 7).

Jerry has honeybees (photo 8) and bumble bees on site to provide pollination services.

Jerry has realized that the winds in Minnesota can play havoc with plastic houses. To provide protection he has surrounded the farm with fast growing trees that slow the wind down (Photo 9). In my opinion, Jerry has been extremely innovative and environmentally sensitive as he goes about producing superior produce.

Adopt a farmer and get a first hand experience of where your food comes from.

Apple Maggots Foiled Again!

Karl Foord, Extension Educator - Horticulture

Karl Foord

Photo 1: Apples showing maggot damage next to protected apple

Karl Foord

Photo 2: Larger apple maggot trapped in nylon guard after exiting apple

Karl Foord

Photo 3: Apple maggot enters apple through flower end and leaves frass

Karl Foord

Photo 4: Small apple cut to reveal resident maggot

Karl Foord

Photo 5: enlarged view of apple maggot resident in small apple


The nylon apple maggot barriers are doing a pretty good job in protecting the apples from the attack by maggots (Photo 1). One fly did manage to oviposit her egg through the nylon mesh. The apple was ruined but at least the maggot was trapped in the barrier sock (Photo 2). Many of the unprotected apples were attacked at the flower end of the fruit (Photo 3). One of these fruits has been cut open to reveal the small apple maggot seen in the lower right half of the right hand slice (Photo 4). Photo 5 is a close up of the same slice. It is obviously critical to get these barriers in place prior to the arrival of the maggots.

The best system would have been to remove all the unprotected apples and give the maggots no chance to feed on any apples. Alas time did not permit. However, it would be best to remove the small damaged apples and get them off-site and not allow the population to build.

Start Trapping for Spotted Wing Drosophila

If you grow raspberries, strawberries, cherries, blueberries, or other susceptible soft-skinned fruit, start a trapping program to monitor the potential presence of spotted wing Drosophila (SWD). A single SWD has been detected on June 6 in a trap set on the University of Minnesota St. Paul campus. Last year, the first SWD was trapped on June 27. It is safe to assume that SWD are present throughout the state.

Jeff Hahn, Univ. of MN Extension

Photo 1: Use traps to detect spotted wing Drosophila's presence.

Home gardeners can monitor SWD with homemade traps. Use a large plastic cup with a cover and make several 3/16th inch diameter holes near the top. Put one to two inches of apple cider vinegar into the cup. Add either a yellow sticky card slightly above the vinegar or a little bit of liquid soap, such as dish soap. Hang traps on branches in a shaded location near fruit. Check traps at least once a week, replacing the sticky card (if used) and apple cider vinegar bait. Dispose of the old apple cider vinegar away from the trap location.

Early detection is very important when dealing with SWD as they can rapidly reproduce to large numbers and damage fruit. Management is a three pronged approach, monitoring (trapping), sanitation, and insecticide treatments. For more information about SWD including management, see Spotted wing Drosophila in home gardens.

Karl Foord, Extension Educator - Horticulture

Karl Foord

Photo 1: Plum Curculio feeding on young apple

Karl Foord

Photo 2: Plum Curculio feeding on young apple fruit

Karl Foord

Photo 3: Plum Curculio feeding hole

Karl Foord

Photo 4: Apple Maggot Barrier protecting young apple fruit from Plum Curculio

The Plum Curculio (Conotrachelus nenuphar) is a pest that may be active now in your apple trees (Photo 1). The first damage caused by these insects is feeding (Photo 2) which creates a small hole (Photo 3). Although this hole is shallow (usually less than 1/8th of an inch, multiple such wounds can affect the quality of the fruit. One way to avoid this type of injury is to place nylon stocking maggot barriers on the fruit (Photo 4). See "A Different Way to Protect your Apples from Apple Maggot". Soon these beetles will mate and you will begin to see a different type of damage caused by the female cutting a crescent -shaped slit into which she will deposit her eggs. See photo 3 in this Plum Curculio Insect Identification Sheet.

The actual size of a plum curculio is @ 1/4 inch long, and the size of the apples in the photos is @ the diameter of a quarter.

Karl Foord, Extension Educator - Horticulture

Karl Foord

Photo 1: Andrenid Bee on Willow Flower




Karl Foord


Photo 2: Andrenid Bee on Prunus flower





Karl Foord


Photo 3: Andrenid Bee on apple flower





Karl Foord


Photo 4: Andrenid Bee and blueberry flowers


Karl Foord

Photo 5: Andrenid bees on raspberry flowers


Andrenid bees are one of the earliest emerging bees in the spring. You can see them on willow flowers depending on the type of spring (Photo 1), and we had such a spring this year. Following willows the Andrenids will often be found on Prunus species (plums & cherries) (Photo 2). The next trees and shrubs to flower are apples (Photo 3), blueberries (Photo 4), and raspberries (Photo 5). Andrenid bees are important native pollinators of these species. The next time you put blueberries on your breakfast cereal or make raspberry jam, remember that Andrenid bees have played a significant role in the creation of those fruits.

Written by Laura Marrinan, University of Minnesota student
HORT 1003 Horticulture for the Home Garden, Spring 2014

Kiwi is a tasty treat that is typically thought of as a tropical or warm climate fruit. However, Minnesota gardeners can get in on the action as well. The practice of growing kiwi in Minnesota has been around since University of Minnesota's Professor Samuel Green began growing cold-hardy varieties in 1892.kiwifruit.jpg

According to Drs. James Luby and Emily Hoover from the University of Minnesota's Department of Horticultural Science, kiwifruit in Minnesota needs to be one of the following species: Actindia kolomikta 'Arctic Beauty', A. arguta 'Bower Berry', or A. polygama 'Silver Vine' (2). These cold hardy kiwifruits don't look like the fruits you typically pick up at the grocery store. They are hairless, skinless and generally have a much higher sugar content. These fruits are also usually about the size of a grape. A. kolomikta can be grown successfully in most areas of Minnesota because it can survive in USDA Hardiness Zone 3, while A. arguta and A. polygma, both are most successful in the central and southern part of the state, USDA Plant Hardiness Zone 4 (2).

Starting your kiwifruit
Kiwi vines can be found at many retail nurseries during the growing season, according to Luby and Hoover. To produce fruit, one male plant is needed for every six female plants. The female plants produce the berries while the male plants are the source of pollen. To differentiate the plant sexes look for at the structure of the plant and the size. The female blossoms have a center pistil to receive the pollen and are usually twice as large, according to an article by horticulturist Victoria Lee Blackstone (1). The male plant will also typically have much larger flowers than the female. Depending on your location, some varietals will be more successful than others (see chart). A. kolomikta is the top performer throughout Minnesota because of its hardiness. This is also a variety that will taste fairly similar to commercially available kiwi (2).

Kiwichart.jpg

According to Luby and Hoover, there are multiple components to consider when starting your own kiwifruit vines. The ground must be fairly sloped and shaded from the afternoon sun. This will help keep the fruit in a moist, cool soil that is preferred by the vines. To help retain moisture, the soil can be covered with wood chips, leaves, or pine needles. This can also help control weeds, retain a consistent temperature and promote healthy roots. Although the soil needs to retain moisture, it is also important to choose a site that is well-drained and porosity (2).

The soil should have a pH of neutral to slightly acidic, around 5.5-7.5 (2). U of M Soil Test Lab Kiwifruit will also benefit from a fertilizer containing nitrogen and the chloride form of potassium. The recommended analysis of fertilizer for kiwifruit is 33-0-0, or 33% nitrogen, 0 % available phosphate and 0% soluble potash. This fertilizer should be applied from spring until early July.

Kiwi vines require support. They grow upward in a counter-clockwise direction, so using a pole or trellis will help direct the growth (4). Fencing will also help the vines grow in the proper direction and provide support.

Winter Protection
Protecting kiwifruit during Minnesota winters is important. The onset of winter comes with two major issues for these vines: animals and weather protection. In Minnesota, cottontail rabbits can cause extensive damage to plants when they are looking for food in early winter. Fencing your vines will help prevent hungry rabbits from damaging your plants (2). Rabbits and Trees and Shrubs

Proper shading of the plants is important because of all the direct sunlight and the sun reflected off of the snow. Slipping a burlap sack or spiral wrap over the trunks will help protect your vines from sunscald (4).kiwi wraps.jpg

Sources:

(1) Blackstone, V.() Differences Between Male & Female Kiwi Vines. SF Gate. http://homeguides.sfgate.com/differences-between-male-female-kiwi-vines-45054.html

(2) Luby, J., & Emily, H. (2010, September 10). Plant and Site Selection. Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/selection/

(3) Kiwifruit Berries. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/selection/

(4) McKenzie, J., & Emily, H. (2007). Hardy Kiwifruit in Minnesota Gardens.Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/?s=kiwi

(5) Trunk Wraps. (n.d.). Commercial Fruit Production in Minnesota. Retrieved May 4, 2014, from http://fruit.cfans.umn.edu/kiwifruit/irrigation_fert_harvest/

Karl Foord, Extension Educator - Horticulture

Karl Foord

Exhibit 1: Cucumber flowers

aggie-horticulture.tamu.edu/galveston

Exhibit 2: Cucumber flowers

www.uq.edu.au

Exhibit 3: Male squash bees in squash flower




www.uq.edu.au


Exhibit 4: Male squash bees in squash flower


The plant family Cucurbitaceae contains a number of our favorite garden plants. This includes: cucumbers, watermelon, muskmelon, pumpkins, squash, and gourds. This group is particularly fascinating in terms of its flower morphology. These plants are called monoecious because they have separate male and female flowers on the same plant (Exhibit 1). These flowers are most easily recognized by the shape of the stem below the flower. The stem below the female flower looks like a smaller version of the final fruit (Exhibit 2), and the stem below the male flower remains a single slender stalk.

Cucurbit flowers are short lived flowers that open a few hours after sunrise and are often closed by midday or early afternoon. Both male pollen viability and female stigmatic receptivity are at their highest when the flower opens and for the next few hours. Both pollen viability and stigmatic receptivity decrease significantly as the day progresses. It is important for the female flower to be pollinated as early in the day as possible.

In cucurbits there is one key concept: The quality of the fruit is a function of the number of seeds in the fruit. The number of seeds produced is a function of the number of viable pollen grains deposited on the stigma. The number of pollen grains deposited is a function of the number of visits by pollinators as well as by the type of bee visiting the flower. Expressed as an equation:

Quality of Fruit ~ # of seeds ~ pollen grains deposited ~ # of bee visits & type of bee

Because both male and female sexual parts are not in the same flower, pollen must be transferred from the male flower to the female flower. The pollen is too large and sticky to be transferred by wind and thus requires insect transfer. Bumble bees tend to deposit more pollen per visit than squash bees and squash bees tend to deposit more pollen per visit than honey bees.

To produce quality fruit watermelon need on the average 1,000 grains of pollen deposited, whereas pumpkin, cucumber and cantaloupe need between 300 and 400.

These flowers need to be visited multiple times (@ 10 - 12) by pollinators to achieve satisfactory pollen transfer and seed set.

Like the solanaceous crops in the previous article, these plants prefer higher temperatures and are sensitive to frost. Daytime temperatures in the high 70s or low 80s degrees and nighttime temperatures close to 65 degrees are optimum for seed set and growth. Poor fruit set or misshapen fruit can sometimes be the result of poor weather which has limited pollinator activity leading to poor pollination and insufficient seed set.

Another very interesting thing about squash flowers is that there is a bee that has evolved as a pollinator specific to squash flowers. Surprisingly enough this bee has been named a Squash Bee (Peponapis pruinosa). Another fun thing is that the male squash bees will often spend the night and parts of the day in the protected space created by the squash flower petals (Exhibits 3 & 4). So if you choose to grow squash you get the potential added treat of watching these very interesting bees.

In addition squash bees are solitary ground nesting bees who will often dig their ground nests in the garden near the squash plants. If you find holes in your garden that are a half inch in diameter, it could be the entrance to the squash bees nest. The linked article in the above paragraph has a picture of the entrance to a squash bee nest. If you encounter such a nest in your garden, one option would be to avoid tilling around this nest and encourage next year's squash bees. If you continue to plant squash every year you could end up with permanent residents.

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