TREE TRAINING AND MANAGEMENT OF CLOSE-PLANTED WAL:-JUTORCHARDS.

Part 11. Flower Drop

Kay Ryugo and David E. Ramos

Paul LaVine, William Olson, Joe Osgood and Steven Sibbett

OBJECTIVES

Examine the basis of the pistillate flower drop and seek means uf

reducing or eliminating it.

PROCEDURES

Compare the behavior of orchards in whiL'h abscission is a problem

and those in which it is not. The following parameters were examined:

1) Light intensity in the trees.2) Nitrogen content of buds and the developing shoots.3) Photosynthetic capacity of leaves in the sun and shade and the nitrogen

content of the same leaves.

4) Mineral contents of exposed and shaded leaves.5) Dry matter and nutrient (ontents of catkins and their influence on

flower set. The effect of catkins removal on flower set.

6) Effectiveness of the synthetic cytokinin, benzyladenine.

RESULTS

Pruning of large mature trees increased light penetration and exposure

of lower leaves to solar radiation but did little to restore productivity.

After three years of pruning, the pruned trees did not yield any more

than the unpruned control trees at Williams and Damon Ranch in Gridleyand Wheatland, respectively. However, it was brought to our attention

that where growers removed entire (temporary) trees to allow better lightexposure to the remaining trees, there was a noticeable improvement oncrop size.

Orchards which were pruned annually resulting in good penetration of

light onto the orchard floor, e.g. Chambers and Ramsdale, the flower

abscission was about 20 and 40% respectively. Where light rarely

penetrated the canopy during the day, as at Williams and Damon Ranch,the drop was 65 and 95% respectively. Bud analysis showed that the

nitrogen contents were 3.5, 3.2, 2.9 and 2.4 percent, respectively, inthe above orchards (Fig. 1). Thus, the percent abscission was inversely

proportional to both light and N levels. Previously, we reported thatwhere light was limited in Hartley trees, shoot growth was less than

that where the leaves were well exposed to sunlight. Photosyntheticmeasurements revealed that walnut leaves began to fix carbon dioxide within15 minutes of sunrise and continued until dark. Leaves in the shadestarted later and maintained a low rate of carbon dioxide fixation

for most of the day. lnterestinglv enough, nitrogen content of shadedleaves was lower than those in the sun taken from the same trees.

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----- -- - - - - --

Seasonal changes in calcium, magnesium and potassium contents of leaves

are shown in Fig. 2,3 and 4. Exposure resulted in higher calcium and

magnesium lev~ls but low potassium content. The reasons may be because

Ca, Mg and K are transported to the leaves from the roots but Ca and

Mg remain ther~ while K is re-translocated to the develuping nut or

elongating shoots ",long with sugars which are synthesized in leaves.

Poromet,>r read i Ii~S showed that the stomata on expost>d I eaves were openwider ~r.d transpired (lost water) faster than those on shaded leaves

(Fig.~) Th~ rate of water loss was greatest during the midday.

Specifi( I~~f weight (SLW) which is the weight of a leaf per unit surfacearea lmg/.'m-) was highest in exposed leaves from uncrowded trees andlowest in lh~ inside leaves of crowded ones (Fig. h). These weights

ref leet ltw photosynthet ic activity, the high value indicat ing high

rate uf carbon dioxide fixation. This agrees with our carbon dioxidemeasurements. This is also reflected in the sugar content l)f leaves.

The number of catkins per spur was 0.9 for Chambers, and ).2 and 5.6 for

Williams and Damon, respectively. The low catkin count at Chambers is

due to the f"rcing of catkin abscissionby the adjacentdevelopingnut.Conversely, where the catkin population was extremely high as at Damon

R~nch, th., t~rminal buds abscised. The average catkin weight at maximum

size was <'Ihllllt 350 mg of which 23% was starch and sugars. Thus, a largecatkin populat ion (55,000 per tree) represents a l'onsiderable drainof nutrients to the spur. This would explainwhy removalof all catkinsfrom a Serr tree in Davis resulted in 88% flower set while the 3 adjacent

trees averaged bJ%. The treated tree yielded 83 Ibs. of nuts while the 3

averaged 63 Ibs.

Benzyladenine treatments at the follqwing rates yielded these results:

Orchard o 12.) 25.0 50.0

% Flower Set._--------

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---- --- ----

Williams (Gridley) b 21 20 23

Damon (small trees) 6 7 7 20

Shannon (Tulare) 23 36 59 55

Yie l.j in lbs/tree--Will iams 23 51 68 47

These data seem to indirate that this material works best where the

setting pntential is already good.

CONCLUS IONS

These data indicate that the Serr trees require light and reasonably

high nitrogen content in buds at budbreak to obtain good set of flowers

(low abscission). Exposed leaves not only fix carbon dioxide at a higherrate, they assimilate nitrogen more efficiently. To obtain betterexposure of leaves to the sun, annual pruning is recommended. This

would entail removing those limbs which have begun to differentiate

large numbers of catkins. If trees are kept fruitful by these methods, that is,by pruning and judicious applications of nitrogen, yields should be

stabilized. Where trees tend to get too large, temporary trees shouldbe removed or whisked back to provide the permanent trees sufficient

light. But even the permanent trees ought to be pruned annually.

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6.0.

Nitrogen content of the developing shoot taken from

different orchards with varying amounts of flower dropThe number in ( ) indicate the approximate % abscission

5.0

Chambers (10)

1.0

0.0

1 I 2 6 7 83 4 5

Weeks after budbreak

Figure 1.

_ 'e,~, _""_ '.. _ _. __.,._

9

0.2(/

~-I

u.15

C.10'

0.05

M~ of leaf Calciumr.:r.1 of leaf area

Circles - uncrowderj trpes

Trian~les crowderi trees

Open symbol - outside leaves

Solid symbol - inside leaves

?-/

// ba -- --

April 23 May 7

Pjgure 2.

- -

--

_ _ _ -O/'

--

Sampling Dates

__ __ba----

Y.Ry 31

.......

--

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--

,./,./

--

0/'

,./,./

A------

--A

.June25

0.10

0.08

I-VII

0.06

0.04

0.02

Figure 3.

,

~ of leaf ma~esiwnof leaf area

Circles - \U1crowdedtrees

Triangles - crowded trees

Open symbol - outside leav~s

Solid symbol - inside leaves

0---// ~--

/ ""'i""

P'-6'"

------

April 23 M~ 7

SAMPLING DATES

- /'/'

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-_-6" "

/0/'

",,/'/'

/'"" ""~

",,"

,,"". ""

May31 June 25

-I -,

I.......'"I

2.75

2.45 -

2.15

1.85

1.55

1.25

.- I

% Potassium on dry weight basis

Circles - uncrowded trees

Triangles - crowded trees

Open symbol - outside leaves

Solid sj~bol - inside leaves

/

,6//

~,/ " "

p-/

//

//

/o

April 23

Firllre 4.

Mq,v 7

" " "'~- '-

..........- -. - ..........-. -0_ ...........- ~~-O

~

--

V',y31 June :>5

3:unplinp, Dates

-go()Q)0)

3'I

~ .~I

Q)()c:cd~(J)

'r~CI)Q)

~

20.0

15.0

10.0

5.0

Resistance to water vapor diffusion

Circl0.s - uncrowded trees

Triangles - crowded tre8S

Open symbol - outside lc o,ves

Solid sflnbol - inside leaves

O~

/6

//

l::1 0- - -0- --"6 -

/

- -9-~-_--6

__0- --

3 40.010 11 12 1 ')r.

Figure 5. T:ime of the Day

--------

Specific Leaf Weights (SLW)

10 /0/"

,/'/"

.//"

/"/"

p.//'

,/

,/,/

,//

0/

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1/

01

Circles - uncrowded trees

Triangles - crowded trees

Open symbol - outside leaves

Solid symbol - inside leaves

6

,

~------4

April 23 May7 May 31 June 25

Figure 6.Sampling Dates

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