Agriculture Reference
In-Depth Information
as the alternate hosts for pome fruit rusts. Particularly common and serious
hosts are eastern red cedar, juniper, and incense cedar.
In arid and semiarid regions, rusts are seldom more than an annoyance
and are easily controlled, due to low humidity and a lack of alternate hosts.
In humid areas where the alternate hosts are found wild and in landscapes,
rusts can cause severe damage to susceptible fruit crops.
Symptoms.
Symptoms on fruit crops include scabbed and distorted fruits,
often with bright yellow or orange pustules. Leaves become deformed and
develop brown, necrotic spots on the upper surfaces and powdery yellow
growths beneath. Infected twigs also become deformed. On juniper and cedar
hosts, large galls develop during wet weather. The galls are usually orange
and slimy, often with gelatinous horns or arms. Spores produced on the juni-
pers travel up to about 3 miles to infect fruit crops. Spores produced on the
fruit hosts likewise infect the cedar and juniper hosts.
Management.
The best management strategy is to grow resistant varieties.
Remove alternate hosts on and around your property. Also remove visibly
infected fruit, leaves, and twigs from fruit crops, preferably before they dis-
charge spores in midsummer. For infected cedar or juniper hosts that cannot
be removed, prune out visible galls whenever you see them. When the galls
on the juniper and cedar hosts enlarge and become slimy, they are dischar-
ging spores. At that time, apply sulfur fungicide sprays to your fruit crops.
Pear Decline
Pear decline is caused by the phytoplasma
Candidatus Phytoplasma pyri
.
Phytoplasmas are organisms that have characteristics somewhere between
bacteria and viruses. In this case, the pear decline phytoplasma is trans-
mitted by pear psylla, infected rootstocks, or infected scions. The pathogen
causes the cambium at the graft union to die, preventing new xylem and
phloem from forming. Without these vascular tissues, sugars and other bio-
chemicals produced in the leaves cannot reach the roots. As the roots die, the
