Insects on your seedlings (Part One: Thrips)

A common insect found on seedlings is the thrip (Order Thysanoptera). Don't be deceived by appearances. Though these tiny yellow insects are about the size of an apostrophe, they can cause heavy physical damage to your plants and transmit viruses. The easiest way to manage thrips is to keep them from getting into your plants in the first place. This means checking any plants that you bring home carefully for signs of thrips. To check for thrips, carefully check the underside of the leaves, a tiny (approximately the size of an ",") yellow or brownish slender insect without visible legs or wings. Thrips prefer young, soft tissue and flowers. Pollen is a favorite treat, but they are also found along vein ridges. Even if you see only a single thrip, be sure to treat all the plants in the flat. For every thrip you see there are at least a dozen you don't.

Thrip damage on potato leaves. Notice a group of yellow thrips circled in red.

If no thrips are visible you can also look for thrip damage. Thrips have sucking mouthparts; they pierce the leaf and suck out all the juices in a cell. This will cause leaf cells to die, making young leaves grow in funny shapes and older leaves to have brown patches with a speckled appearance.

A young misshapen pepper leaf. The thrip damage has killed the cell at the end (red circle) and the leaf can't expand properly.

To treat for thrips you can use biological controls, such as the predator mites found in Thripex (http://www.koppert.com/pests/thrips/), insecticides, a simple soap solution. If you use soap be sure to douse the plant (preferably dip them in a bucket) to make sure that all the nooks and crannies in the plant have been treated. If you'd like to know more about thrips or insecticides you can use? Check out this information sheet from UC Davis: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7429.html

Thrip on pepper flower.

Test garden results 2013

February has come, and with it a deluge of seed catalogs. Each one promising better yields, more flavor and bigger produce if you just pick the right variety. As some of you know, when I started the 2013 gardening season I decided to grow a smorgasbord of vegetables and varieties to find good options for growers with small spaces. Many delicious varieties exist, but if space is limited you want the most you can get out of your space. Before I start telling you my favorites or least favorite a quick disclaimer is necessary. In many cases, these varieties were not replicated in multiple locations and I did not collect metrics such as total number of fruits or plant height. What you will hear are how the varieties performed relative to each other, in terms of productivity, earliest fruit, how soon I saw disease, space, and flavor. These are the results of my test gardens:

Turnips and greens
Purple Globe turnip: Early producer with good flavor... extremely susceptible to wireworms.
Lettuce: Bolted early in the summer heat
Spinach: Bitter flavor, but was likely due to the summer heat

Beans and peas
Purple, Green, Yellow mix: Highly slug susceptible, very prolific, and good flavor
Peas

 Tomatoes*
* Tomatoes were grown in three locations (a home garden in Royal Oak, a home garden in Lansing, and a community garden in Lansing)

		Variety
	Location	Banana Legs	Tigerella	Indigo Rose	Snow White
Productivity	Royal Oak	Moderate	Moderate	High	*
	Lansing	Low	High	Moderate	High
Flavor	Royal Oak	Mild flavor, a bit mealy	Slightly sweet and juicy	Good flavor, meaty tomato	*
	Lansing	Bland with mealy texture	Average flavor, quite juicy	Good flavor	Excellent flavor, very sweet, low acid
Color	Royal Oak	Bright yellow	Orange with yellow stripes	Red and Purple	Pale yellow
	Lansing	Bright yellow	Orange with yellow stripes	Red and Purple	Pale yellow
Maturity	Royal Oak	Late	Early	Late	*
	Lansing	Mid-Season	Early	Mid-Season	*
Septoria	Royal Oak	*	*	*	*
	Lansing	None	Highly Susceptible	None	None
Cracking	Royal Oak	None	Minor	Minor	*
	Lansing	None	Highly Susceptible	None	Minor
Size		3-4"	1-1 1/2"	2"	<1"

Tigerella tomato (you can see a growth crack on the left)

Indigo Rose tomatoes

Squashes
Spaghetti squash: mid-sized vines, good production
Early acorn hybrid: very prolific, moderate plant size with good acorn squash flavor
Greyzini zucchini: Long gray and green fruit, extremely prolific, of the three zucchini varieties this was the last to get powdery mildew

Early Acorn hybrid squash

Pumpkins
Lil' Pump-ke-mon hybrid: Prolific, bushy pumpkin with small (3" wide) yellow and white fruits
Fairytale: a mid-sized flattened pumpkin with mahogany color, the flesh is supposed to be tasty, but mine were stolen

Cucumbers
Burpless Beauty: highly susceptible to downy mildew, good yields, good flavor, compact vines
Burpee Pickler hybrid: highly susceptible to downy mildew, good yields, good flavor, compact vines

Carrots
Cosmic purple, good flavor, no disease or insect damage visible

Ali Baba Watermelon fruit

Delice de la table Melon

Green Nutmeg Melon

Melons
Green Nutmeg: late maturity, moderate production, tiny fruit, highly susceptible to downy mildew
Golden Midget watermelon: low fruit set, flavor is mediocre, weak and sprawling vines, small fruit
Ali Baba watermelon: average flavor, sweet, moderate production, mid-sized melons
Delice de la table melon: good flavor, good production, sprawling vines

Leaves and vines of Golden Midget Watermelon

Golden Midget Watermelon (it's about 8" long)

Potato
Purple Peruvian: Vigorous plants, good production, fingerling potatoes with average flavor


I'm excited to see what 2014 brings us!

So much diversity!

Fall is coming to a close, and with it the end of another gardening season. The storeroom is filled with acorn and butternut squashes, onions are collected and potatoes are all dug up. For those of you lucky enough to have a greenhouse or low tunnels the season is still going, but for the rest of us it's time to clean, compost, prepare and wait til next year's gardening begins.

I'll be spending the winter months talking about a slew of topics from varieties in my test garden to insects. The first topic I want to talk about is diversity, and the amazing variation that is available to gardeners.

Apples (bottom) and grapes (top) from around the world in different size, shapes, colors and textures.

This past September I had the opportunity to drive to the USDA ARS germplasm center in Geneva, New York with my good friend Joseph Tychonievich. For those of you who don't know what a germplasm center is, it is a facility dedicated to the maintenance and preservation of genetically diverse plant material. Before commercialization of fruits and vegetables, people selected plants for flavor, texture, color and winter storage, not for traveling, uniform ripeness and some of these other traits that current varieties of fruits and vegetables have to meet. There were hundreds of varieties of melons, tomatoes, cucumbers, carrots, broccoli, etc. Germplasm centers are facilities that maintain the "heirloom" varieties, but they also have wild and unadapted relatives that might not be tasty, but are good sources to breed in disease resistance and other traits. The United States Department of Ag has a number of germplasm centers across the U.S. The center in New York contains apples, grapes, tart cherries as well as some vegetables like tomatoes. In their apple catalog alone there are 100s of cultivars of apples from all over the world as well as wild species from Kazakhstan.

A young apple forest at the germplasm center. You can see the ground is littered with hundreds of fallen apples. Each tree in this block is from a single seed and is therefore genetically diverse from all the other trees around it.

Apples (Malus spp.) originated in Kazakhstan, and in some parts of that country old apple forests still remain. It is from these forests that apples were brought to the rest of the world and selected until they became the apples varieties that we have now. I had two goals when I visited the germplasm center:  1) Try as many apples as I could and 2) Bring back seeds to plant my own apple forest. 

This apple species had beautiful color, the flesh was an orangish red once you cut it open. The taste was a little too bitter for my taste, but it was one lovely apple!

These are all wild species apples from Kazakhstan. The one on the far left is about the size of a Golden Delicious. This was just a sampling from a couple of the trees that were there.

Even the flesh color of these apples had diversity!

Some of the varieties we tasted were amazingly delicious! Others... let's just say they were reminiscent of old gym sock. We tried fruit from related species, that was so bitter and astringent it made your tongue numb. The textures of the fruit were incredible too, with some being mushy and grainy while others were crisp and light. The diversity in apples is amazing. I had no idea that so many varieties existed. There was even one apple variety that tasted almost "meaty" to me.

While I did bring back a lot of seeds, none of these will be the exact same as the apples from which I took them. Some plants are self-pollinated and their seeds will be just like the parent plants, others are only cross-pollinated. Apples are cross-pollinated and each seed is distinct and unique having some combination of genes from its parents. All apple varieties are maintained through cuttings called scions that are grafted onto rootstocks.

Breeding a new delicious apple variety takes a bit of luck and a lot of patience. While none of the apple seeds I planted might end up being the next Honeycrisp, they are a treasure trove of diversity and I'm excited to see what will grow.

This apple seedling came from a Gala I bought at the grocery store. You don't have to go to New York to find apple diversity, it is right in your local supermarket. Remember, apples are cross-pollinated so each seed is unique.

Cucurbit downy mildew

Believe it or not another mildew exists that attacks your cucumbers, squashes and melons. It’s called cucurbit downy mildew. Powdery mildew and downy mildew are two different diseases caused by two very different pathogens. Whereas powdery mildew is caused by a fungus, downy mildew is caused by an oomycete, Pseudoperonospora cubensis. For some of the differences between oomycetes and fungi see the post on late blight.

Cucumber plants with downy mildew in a garden plot. You can see the yellowing foliage.

Similar to powdery mildew, downy mildew is caused by an obligate pathogen that requires a living host. It only affects the leaves of the plant; not the roots, stems or fruits. Don’t be fooled into thinking this won’t do much damage however. It turns out that downy mildew is a huge problem, especially on cucumbers. Commercial growers spend hundreds of dollars each year trying to manage this disease, and it can still cause crop losses. This pathogen is dispersed by the wind and can be blown up from the south or down from greenhouse grown plants in the north. The pathogen infects the leaves, begins to take nutrients away from it. Leaves will die, any fruit that are produced will typically be deformed, and the plant will eventually die.

Close up of a single leaf. The yellow patches on the leaf are downy mildew and will eventually turn necrotic as the disease progresses.

Symptoms

The symptoms differ depending on what type of cucurbit it’s on. On cucumbers you typically see very angular lesions, and they will be restricted by the veins. During early stages of infection the leaves show watersoaking which progresses to yellow angular patches. As the infection progresses those angular lesions become necrotic (dead) and if you look on the underside of the leaf will be hundreds of tiny grayish sporangia. They are too small to see well with the naked eye, but it will look like grayish dirt on the underside of the leaf. On melons, the lesions are more rounded, have a cholorotic (yellow) halo and can easily be confused with other leaf diseases (like Alternaria).

This is the underside of that same leaf. You can see the lesions being restricted by the small veins, and if you look closely you can see the grainy appearance of those sporangia inside the lesions.

Management

Unfortunately there aren’t a lot of cultural (or non chemical) controls for downy mildew. There are no varieties currently available with complete resistance to the pathogen, but some varieties are more susceptible than others. (Ask your local extension agent for varieties that are least susceptible in your area). Start cucumbers indoors to maximize their production time. You can slowdown the effect of the disease by scouting for symptoms. Often downy doesn’t show up until the end of July/early August when the weather is warm (not hot), and humid. Some years, if conditions are good, the disease has been seen in Michigan as soon as the first week of July. The Michigan State University Extension service puts out a notice as soon as downy mildew is detected in the surrounding states. They also have some information for home gardeners, I really like the pictures of the sporangia. The pathogen infects and spreads best in warm humid conditions. So, having good plant spacing and limiting your overhead watering can make the microclimate in your canopy less favorable for disease. If you catch the disease early enough you can remove infected tissue by double bagging it, and putting it in the city trash.

Downy mildew on a cantaloupe. The lesions aren't quite as angular and they have a yellow halo around each one.

So does this mean you should give up on cucumbers? Absolutely not! Start those seeds indoors, space your transplants adequately, scout often, and you'll still have a perfectly decent cucumber harvest.

Source contributing information:

http://ohioline.osu.edu/hyg-fact/3000/pdf/3127.pdf

http://msue.anr.msu.edu/news/downy_mildew_spores_detected_in_michigan

http://msue.anr.msu.edu/news/managing_cucurbit_downy_mildew_in_your_garden

Late blight

When people hear the term late blight, panic often ensues. Late blight brings to mind the Irish potato famine and rotting potatoes. For others, late bight is the kiss of death for their tomatoes. In the U.S. alone, dozens of scientists study late blight and how to manage it. But what is it? And why is it so terrible? Unfortunately, or fortunately, I have never had late blight in my own tomatoes so the only picture I have available is a fruit I found in a research plot.

Late blight is caused by the oomycete pathogen Phytophthora infestans. For those of you who haven't heard that term before oomycetes are almost something between a fungus and an alga. They are more closely related to algae, and are frequently called watermolds, but they have hyphae (those thread-like strands fungi produce) and they also produce tiny spores called sporangia. P. infestans is spread through the air. Its tiny spores are easily caught by wind currents and carried from field to field.

Symptoms

Late blight starts as small watersoaked lesions that rapidly grow,  and turn brown as the tissues die. When conditions are suitable, fluffy white growth can be seen on the dead tissue. Lesions spread, causing leaves and stems to shrivel and die. Lesions occur most frequently on the stems and leaves, but infections can also be seen on the fruit. On green fruit the lesions have a greasy look and are brown. Lesions on the mature fruit can sometimes have a ringed appearance.

A mature late blight lesion on a ripe tomato fruit. You can even see the growth rings.

Disease cycle

Early during the growing season the pathogen infects a susceptible host.  The predominant susceptible hosts for late blight are going to be potato and tomato. The disease cycle begins when a spore lands on a susceptible host and infects the tissues. At first, the pathogen doesn't seem to be dangerous. It steals some nutrients, but nothing much, and just as your plant is realizing that something isn't quite right..... the pathogen takes off. It starts destroying cells, dissolving cell walls, breaking down sugars, and eating the juices inside. Even susceptible plants try to fight back, but the pathogen has too large of a head start. As the disease progresses, large dark necrotic (dead) spots appear on the leaves and stems of the plant, these eventually have white fluffy growth on them. If you could look very closely (even a hand lens isn't enough) you could see little tiny white sporangia. These are the spores that will fly off and infect new plants. The pathogen can overwinter in crop debris, tubers or fruit.

You might be asking yourself, what chance do you have against something like this?

This is where research comes in. Dozens of researchers around the world study P. infestans. How it infects, how plant can resist it, what management practice work, which ones don't work; they even have tracking systems so you can see how late blight moves through an area.  Plant breeders are constantly working to develop varieties (tomato and potato) that are resistant to late blight. Unfortunately, the pathogen is always adapting to infect the plant.

Management

P. infestans can overwinter in the crop debris (potato tubers, tomato stems and fruits) so cleaning your plots is imperative for disease prevention the following year. The only management that traditional gardeners have that organic growers do not is chemical controls. For home gardeners, products like Ortho multi purpose fungicide, Acme Tomato and Green Light Maneb Plus contain effective active ingredients and are labeled for home grower use. If choosing to use a chemical control be sure to read the label and follow all safety rules and regulations for use. All other strategies are in the organic management section.

Organic management

Organic growers have few options for managing the disease once they have it. No organic chemistries or plant extracts have been shown to be consistently effective in controlling late blight. Copper, a staple for most organic management programs provides minimal control. Prevention is really the best way to manage the disease.

Starting with clean materials (tubers or transplants) is the first step. During planting, keeping plants properly spaced will help improve airflow and keep leaves dry. Watering plants from the base vs. overhead watering can reduce moisture on the leaves (Hartill et al. 1990). Similar to many pathogens, P. infestans requires a few hours of leaf wetness before it can germinate and infect the host. If you see the disease while scouting (cite scouting page), removing the infected plants  (double bag and put into the trash NOT the compost), will help reduce the levels of spores. At the end of the growing season be sure to remove all susceptible plant material, regardless of whether it had visible symptoms or not.

Crop rotation is effective for managing late blight, but you will need to rotate with a nonhost for at least 3 years. Late blight resistant varieties of tomatoes exist, and while they are not ideal for commercial gardens, they happen to be perfectly tasty for home gardeners. These include varieties like Mountain Magic, developed by an NC State tomato breeder, and Plum Regal.

Late blight can be difficult to manage, and is likely a disease you hope you never get. With proper scouting, culling and sanitation the losses of this disease can often be minimized.  If you do have late blight, contact your local extension agent immediately for the most up to date (and effective) control strategies for your area. If you don't have an extension agent click here for USAblight, a national site for late blight information.

For Fungicide Options: http://articles.mcall.com/2012-06-29/entertainment/mc-tomato-late-blight-treatment-prevent-20120629_1_late-blight-irish-potato-famines-spore-spread

Rubin E, Baider A., Cohen Y. 2001. Phytophthora infestans producs oospores in fruits and seeds of tomato. Phytopathology 91:1074-1080

Hartill WFT, Young K, Allan DJ, Henshall WR. 1990. Effects of temperature and leaf wetness on the potato late blight. New Zealand Journal of Crop and Horticultural Science 18:181-184

Dorn B, Musa T, Krebs H, Fried PM, Forrer HR. 2007. Control of late blight in organic potato production: evaluation of copper-free preparations under field, growth chamber and laboratory conditions. Eurpean Journal of Plant Pathology 119:217-240

NC STATE Extension bulletin on disease managemenet, chemistries and resistant tomato lines: http://www.cals.ncsu.edu/plantpath/extension/fact_sheets/Tomato_-_Field_Staked_-_Late_Blight.htm

Cornell University Extension bulletin on management and resistant varieties: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Tom_LB_OrganicMgt10.html - Plum Regal