الآفة النباتية على الساق.

A careful MSA pronunciation is:

al-ʾāfatu n-nabātiyyatu ʿalā s-sāqi

A few useful notes:

• الآفة = al-ʾāfa(tu)
• النباتية is pronounced an-nabātiyya(tu) in full, because ن is a sun letter, so the l of ال assimilates.
• الساق is pronounced as-sāq(i) for the same reason: س is also a sun letter.

In slower learner-friendly transliteration, you can think of it as:

al-aa-fa tun na-baa-tiy-ya tu ʿa-laa s-saaqi

Because Arabic often leaves out the present-tense to be.

So:

• الآفة النباتية على الساق
  literally = The plant disease on the stem
• natural English = The plant disease is on the stem

This is a very common Arabic structure called a nominal sentence. In the present tense, Arabic usually does not say is / am / are.

Because النباتية is an adjective describing الآفة, and Arabic adjectives normally agree with the noun they describe in definiteness.

So:

• الآفة = the disease / the blight
• النباتية = plant-related / botanical / vegetal

Since the noun is definite, the adjective must also be definite:

• الآفة النباتية = the plant disease

Compare:

• آفة نباتية = a plant disease
• الآفة النباتية = the plant disease

Here it is an adjective, not an iḍāfa (genitive/possessive construction).

So الآفة النباتية means:

• noun: الآفة
• adjective: النباتية

Why we know it is an adjective phrase:

• both words are definite
• the second word matches the first in gender and definiteness
• the meaning is descriptive: plant / botanical disease

If it were an iḍāfa, the structure would look different.

Because الآفة is feminine, and Arabic adjectives must agree with the noun in gender, as well as number and definiteness.

So:

• آفة is a feminine noun
• therefore the adjective must also be feminine
• نباتي = masculine
• نباتية = feminine

That is why you see the feminine ending ـة in النباتية.

على means on / upon.

الساق here means the stem or the stalk in a plant context.

So:

• على الساق = on the stem

A useful vocabulary note: ساق can also mean leg or shin in other contexts. Arabic words often have several related meanings, and the surrounding words tell you which meaning is intended. Since this sentence is about a plant problem, الساق here is understood as stem/stalk.

Because it comes after the preposition على.

In Arabic, a noun after a preposition is normally in the genitive case, so in fully vowelled MSA you would read:

الآفةُ النباتيةُ على الساقِ

So:

• على = preposition
• الساقِ = genitive after the preposition

In normal unvowelled writing, you usually do not see the final kasra, but grammatically it is still there.

In careful fully vocalized MSA, the sentence is:

الآفَةُ النَّبَاتِيَّةُ عَلَى السَّاقِ

The endings are:

• الآفةُ → -u because it is the subject/topic of the nominal sentence
• النباتيةُ → -u because it is an adjective agreeing with الآفة
• الساقِ → -i because it follows the preposition على

At the end of a sentence, many speakers pause and do not pronounce the final case ending clearly, especially in less formal speech.

It is a nominal sentence made of:

• a noun phrase: الآفة النباتية
• a prepositional phrase: على الساق

So the structure is basically:

• topic / subject: الآفة النباتية
• predicate / comment: على الساق

In other words:

• The plant disease → what about it?
• It is on the stem

This order is the most straightforward and natural for a simple statement:

الآفة النباتية على الساق

It starts with the thing being talked about, then gives information about it.

Arabic can sometimes change word order for emphasis or style, but for a basic learner sentence, this order is the normal one.

It can have a wider range of meanings depending on context, such as:

• blight
• pest
• affliction
• scourge
• damage-causing problem

In agricultural or plant contexts, it can refer to a harmful condition or pest affecting a plant. So even if your translation gives one English meaning, it is useful to know that the Arabic word can be a bit broader.

You would remove ال from the noun and adjective:

• آفة نباتية على الساق

This would mean:

• a plant disease on a stem
• or, depending on context, a plant disease on the stem

In full case endings, it could be:

آفَةٌ نَبَاتِيَّةٌ عَلَى السَّاقِ

So the definite version and indefinite version differ clearly in Arabic.

Because Arabic and English package information differently.

A very literal breakdown is:

• الآفة = the disease / blight
• النباتية = plant-related
• على = on
• الساق = the stem

But natural English usually prefers something smoother, such as:

• The plant disease is on the stem
• or The blight is on the stem

So when learning Arabic, it helps to understand both:

• the literal structure
• the natural English meaning