Feeds:
Posts
Comments

Posts Tagged ‘Fire blight’

In the warmth of our early spring, landscapes burst with enthusiasm for the season; trees and perennials woke up in a raucous, flower-filled welcome.  Gardeners greeted the spring show with joy, but as plant after plant sent forth blooms we soon went from feeling euphoric to feeling alarmed.

“Wait, wait, it’s only March,” we muttered at forsythia, and “you’re not supposed to be here until Mother’s day,” we told lilacs.  Crabapples ushered in April instead of May while flowering bulbs burst open in a display more like the fireworks finale than a long, colorful parade.

Sure, it was nice, but also disturbing.  After all, Mother Nature has a way of laughing at Colorado.  And this year, she’s in a full belly-laugh, sending snow and freezing temperatures just as we brought out our Hawaiian shirts and flip flops.

The start of our season was weeks ahead of schedule, with horticulturists and gardeners noting a three-week earlier flowering or leafing out.  Diseases and insects emerged early too, making things busy for landscape and tree maintenance companies.

Experts use phenology, or Degree-day models, to predict pest outbreaks; it’s based on the number of days or hours at certain temperatures the pest needs to emerge after winter.  Depending on the pest, we’re eight days to one month ahead of the usual pest problems.  The Emerald Ash Borer began popping from trees at the beginning of May; last year (the first season tracked following its detection here in Colorado) it emerged in early June.  The bug isn’t getting more aggressive, it’s simply following the climate we’ve had this year.

Gardeners should be aware that many pests are active earlier.  And although the recent cold weather might have put a crimp in their activities, those pests are resilient.  Controlling pests before their damage is severe is the best way to sustainably garden, so be on the lookout for potential problems and have your strategies in place to keep your plants healthy.

Here are a few thugs to watch for:

Fire blight is a bacterial disease that’s destructive to apple, pear, quince and crabapple. It attacks in spring, when temperatures reach 65 degrees F and frequent rain occurs. The best weather conditions for this damaging disease is exactly what we just had: humidity, rain, and hail.  This is when masses of bacteria are forced through cracks and bark pores to the bark surface, where they form a sweet, gummy exudate called bacterial ooze.

Insects attracted to this ooze pick up the bacteria on their bodies and carry it to opening blossoms or young branches wounded by pruning, insects, or hail. Girdling cankers – areas of disease on the wood – develop from branch or blossom infections.  Leaves wilt, darken, and curl into a shepherd’s crook. This gives the tree a fire-scorched appearance, thus the name “fire blight.”

There’s no cure for this disease; prevention is the best solution. Fire blight control include use of resistant varieties, cultural practices, pruning and spraying.

Japanese beetles are beautiful but devastating insects that attack over 300 types of plants, including grapes, raspberries, beans, apples, and roses.  Ganging up on plants, they cause serious injury.  Louisville, Lafayette, and Boulder residents have reported the beetles; it’s unclear how widespread they are in our area.  For more information on Japanese beetles and their control, see ext.colostate.edu/pubs/insect/05601.html.

Gardeners with strawberries, raspberries, and other cane fruit should watch for Spotted Wing Drosophila (Drosophila suzukii).   The overwintering females of this fruit fly relative lay hundreds of eggs on ripe fruit.  Upon hatching, the larvae burrow inside, where they feed on the fruit, growing into plump maggots.  According to the Degree-day models, we’re rapidly approaching peak egg laying by overwintering females and the first emergence of this season’s adults.

From egg to adult is a mere eight to ten days, depending on temperatures, and there are several generations per year.  Keep your fruit meticulously cleaned from the floor of the garden and pick and discard overripe fruit.

Advertisements

Read Full Post »

Today’s post can be heard on the public radio show Crop to Cuisine, hosted by Dov Hirsch.

There’s a thug lurking in your neighborhood, taking every opportunity to attack your precious tree fruit.  With oozing droplets and a hoard of unwitting helpers, it moves from tree to tree, torching twigs and branches until the tree looks scorched.  Evidence of the infection becomes more obvious as we head into June.

 Fire blight is a bacterial disease that affects certain plants in the rose family. It is especially destructive to apple, pear, quince and crabapple. It attacks in spring, when temperatures reach 65 degrees F and frequent rain occurs, and then bacteria overwintered in cankers on the tree resume activity, multiplying rapidly.

 Though the good news is that we’ve had some rain and humidity, the bad news is:  the recent weather created good conditions for this damaging disease.  This is when masses of bacteria are forced through cracks and bark pores to the bark surface, where they form a sweet, gummy exudate called bacterial ooze.

 Insects such as bees, ants, flies, aphids and beetles are attracted to this ooze, pick up the bacteria on their bodies, and inadvertently carry the bacteria to opening blossoms. Bacterial ooze splashed by rain also can spread the disease.

 Young branch tips can be infected through air openings on leaves, called stomata, air openings on branches, called lenticels, or, more commonly, through wounds created by pruning, insects, or hail storms.

 Droplets of ooze can form on these infected twigs within three days and fruit may be infected through insect feeding wounds. Girdling cankers – areas of disease on the wood – eventually develop from branch or blossom infections.  Leaves wilt, darken and curl to form a shepherd’s crook. This gives the tree a fire-scorched appearance, thus the name “fire blight.” 

 There is no cure for this disease, so prevention is the best solution. Fire blight control methods include use of resistant varieties, cultural practices, pruning and spraying. Using resistant varieties is the most effective prevention method, but keep in mind that resistance doesn’t mean immunity.

 Remove and destroy newly infected young twigs as soon as possible, so that your tree doesn’t become the mother ship for disease in the neighborhood.   Do this when no rain is predicted for at least two weeks.   It may be best to leave pruning until winter when the bacteria are not active. This reduces infection on the tree and the number of bacteria available to infect healthy blossoms and shoots.

 In young twigs, make cuts at least 12 inches below the dark, visible edge of infection to avoid slicing into the bacteria. Remove all blighted twigs and cankered branches. Prune larger limbs about 6 to 12 inches below the edge of visible infection.

 After each cut, surface sterilize all tools used in pruning. Spray tools with Lysol or dip tools in 70-percent ethyl alcohol, or a 10-percent bleach solution.  Bleach can rust tools, so if you use this to sterilize your pruners, wash them after you’re done and apply a light tool oil to keep them rust-free.

Read Full Post »