Tuaian itu kecil bukan kerana pendebungaan gagal, tetapi kerana banyak perosak.

In Malay, demonstratives like ini and itu usually come after the noun:

• tuaian itu = that harvest / the harvest in question
• rumah ini = this house

So tuaian itu is the normal Malay word order, not itu tuaian.

Malay often leaves out the equivalent of the verb to be when linking a subject to an adjective or noun.

So:

• Tuaian itu kecil literally looks like that harvest small
• but naturally means That harvest was small or The harvest was small

This is very normal in Malay. You do not need adalah here.

Yes, kecil literally means small, but Malay often uses it more broadly than English does.

With tuaian or similar words, kecil can mean:

• small in amount
• poor
• low-yielding

So Tuaian itu kecil means the harvest was small/poor, not necessarily physically tiny.

This pattern means:

• not because ..., but because ...

So:

• bukan kerana pendebungaan gagal = not because pollination failed
• tetapi kerana banyak perosak = but because there were many pests

It is a very common contrast structure in Malay.

You can think of it as:

• bukan X, tetapi Y = not X, but Y

Both bukan and tidak are negatives, but they are used differently.

A useful basic rule:

• tidak usually negates verbs and adjectives
• bukan usually negates nouns, noun phrases, and often whole contrasts like not because X, but because Y

In this sentence, bukan kerana ... tetapi kerana ... is a fixed and very natural pattern, so bukan is the correct choice.

Pendebungaan means pollination.

It is built from debunga related to pollen, with affixes that create a noun referring to the process. For a learner, the important thing is simply:

• pendebungaan = pollination

So:

• pendebungaan gagal = pollination failed / failed pollination

In Malay, adjectives and many stative verbs typically come after the noun they describe.

So:

• pendebungaan gagal = failed pollination or literally pollination failed

Malay does not usually put gagal before the noun the way English can say failed pollination.

Compare:

• rancangan gagal = a failed plan
• usaha berjaya = a successful effort

It can suggest either, depending on how you translate it into English.

Malay often allows a phrase like this to feel both:

• like a small clause: pollination failed
• and like a noun phrase: failed pollination

In your sentence, the meaning is basically not because pollination failed.

Malay often omits words that English requires if the meaning is already clear.

So:

• kerana banyak perosak literally = because many pests
• naturally in English = because there were many pests or because of many pests

Malay does not always need ada here.

If you said kerana ada banyak perosak, that would also be understandable, but the original sentence is more concise and natural in formal writing.

It can be either, depending on context.

Malay nouns usually do not change form for plural:

• perosak = pest / pests

Here, banyak makes it clearly plural:

• banyak perosak = many pests

Perosak means pest—something harmful that damages crops or plants.

It comes from a root related to damaging or ruining, so perosak is literally something like a destroyer/damager, but in normal usage it means pest.

In an agriculture context, that is the most natural translation.

Yes, in many everyday contexts sebab can replace kerana.

For example:

• bukan sebab pendebungaan gagal, tetapi sebab banyak perosak

That would be understandable and natural in conversation.

However:

• kerana sounds a bit more formal or written
• sebab sounds more conversational

So the original sentence has a slightly more formal, explanatory tone.

Repeating kerana makes the contrast very clear and balanced:

• bukan kerana X, tetapi kerana Y

This is a common and neat structure in Malay. It is similar to English repeating because in:

• not because X, but because Y

You could sometimes restructure the sentence, but the repeated kerana is perfectly normal and stylistically clear.

Yes. That is a very natural English translation.

The final phrase:

• kerana banyak perosak

could be rendered as:

• because there were many pests
• because of many pests
• because of pest pressure (more technical/agricultural)

The exact English wording can vary, but the Malay structure stays the same.

Yes, it sounds fairly neutral to formal, especially because of words like:

• tuaian
• pendebungaan
• kerana
• perosak

This feels like something from a report, explanation, article, or textbook rather than casual spoken Malay.

In everyday conversation, people might choose simpler or more colloquial wording.