Walnuts

• Walnuts are a monecious plant which means that the male and female flowers are on the same plant
• Walnuts are wind pollinated
• Female flowers form in small clusters
• Male flowers are called staminate and form in catkins which have hundreds of staminates
• Terminal bearers only produce fruit on the terminal buds
• Lateral bearers only produce fruit on the tips of spurs and long shoots
• Lateral bearers include Chandler, Chico, Howard, Payne
• Dichogamy means that everything on the plant does not happen at the same time (male flowers before female flowers)
• Protandrous means that the male flowers bloom first and then the females, this is most walnuts
• Protogynous is when the female flowers bloom before the males, this only happens in Chico, Forde, and Ivanhoe
• The problems with hand pollination is that the pollen dries out and becomes not viable, pistillate flower abscission, andare backline
• Pistillate Flower Abscission is when the flowers abscise despite sucessful fertilization, it is caused by too much pollen, can result in up to 95% crop loss, and Serr is very susceptible
• PFA is when the excess pollen causes ethylene to be produce and causes fruit drop
• PFA can be avoided by using ReTrain which is a PGR
• ReTrain inhibits ethylene production to decrease PFA
• ReTrain is very expensive, can't be tank mixed, and is not organic
• ReTrain 1st spray is applied at 30-40% pistillate bloom. 2nd spray if expecting high PFA
• Blackline is a virus that travels slowly through the walnut and kills the graft union
• Blackline is spread through grafting and pollen
• Early infections of blackline are asymptomatic
• Black walnut and Paradox rootstocks are most susceptible to backline
• Blackline is more common in hand pollination because of the excess moving around of pollen
• Flower initiation is when the parts of the flower are being formed
• Flower initiation starts when bloom is coming to an end, then stops while fruit enlarges and develops, and then stats again in spring when bloom is about to begin
• Walnuts need a lot of chill time below the threshold temperature
• Late leaf out means high chill requirements
• Chill requirements range from about 400-1600 hours across all cultivars
• A low chill requirement is Serr with 650 hours
• A medium chill requirement is Pedro with 800 hours
• A high chill requirement is Harltey with 1000 hours
• The ovule develops into the seed/kernel
• The kernel is entirely composed of the ovary and no endosperm remains
• The ovary wall develops into the shell
• The surrounding involucre and sepals develop into the hull and husk
• At 30% open the female flowers are at their peak receptivity
• When female flowers are 100% open they are not viable because they have too much air contact
• If a fruit is successfully pollinated, the stigmas will fall off the tips, if it was unsuccessful the stigmas will stay attached
• If you have poor pollination then change your pollinizer cultivar or increase the amount of pollinizers in your orchard
• Fruit growth: Lag phase -> exponential growth (4-8 wks) -> plateau -> second exponential growth phase -> plateau (16-20 wks)
• During the first plateau in fruit growth the shell is hardening and the kernel is rapidly growing